For the most part, each settlement usually has two trainers. You can occasionally get some skills for free or from people who aren't full trainers, but as far as I can tell every skill is learnable somewhere from somebody.

You only have 3 unlocks of special skills, which are the ones in the middle of the skill table that cost 500 silver. You have to unlock this skill to unlock the higher tier skills which cost 600 silver. I have yet to find any way to increase the amount skill points you get, but if somebody has please let me know. I've denoted the skills which use those skill points as point skills because I'm really clever. The skills listed before the point skill are all the unlockable ones, the ones after the point skills require it.

The lowest level of skills cost 50 silver, then the ones above them usually cost 100. Then 500 for the "skill" skill, and 600 for the top tier ones.

Keep in mind that if a skill branches off into two options, such as in the runic magic skill tree, you can only pick one of those options. So in runic magic you can only have increased rune effects OR casting runes without a lexicon.

This is a WIP, I'll be adding others as I go along. Big thanks to Miria in the comments for helping and putting together a pretty great list of all the skills.

Chersonese is a bit unique in that there's only 1 trainer in the city, the other is the wind hermit. To get to him travel through the fort just a bit north of the mountain and go through it to get to the Wind Cabal temple and he's in there.

Kazite Spellblade, Cierzo

• Steady Arm: Increases Impact resistance by 15 while you are blocking.
  
  
• Shield Charge: Stamina cost 15, cooldown 30. Requires shield. Rush forward to hit foes with your shield for high impact. Can hit the target twice and inflict the confusion status effect.
  
  
• Fitness: Increase your max health by 25 and the amount of health you restore by sleeping by 20%.
  
  
• Point Skill - Spellblade's Awakening: Increase your max health, stamina, and mana by 15 each.
  
  
• Infuse Fire: Mana cost 15. Requires warm boon. Temporarily adds fire damage to your melee weapon and inflicts burning on enemies. Consumes your warm boon.
  
  
• Infuse Frost: Mana gost 15. Requires cold boon. Temporarily adds frost damage to your melee weapon and inflicts Slow Down on enemies. Consumes your cool boon.
  
  
• Elemental Discharge: Mana cost 15, cooldown 10. Requires infused weapon. Shoot a projectile of the element that is infused on your weapon.
  
  
• Gong Strike: Stamina cost 11, Cooldown 30. Requires infused weapon and shield. Strike your weapon on your shield, removing the elemental infusion to make an explosion of that element.

Cabal Hermit, Chersonese.

Note that some of the Cabal skills require activated wind altars, there's one in each area. The one in Chersonese is just next to the temple, the one in the desert is also close to its temple. The one in Emmerkar Forest is inside of Bege on top of a wall by the gate. The swamp pillar is right along the pilgrims path at the Cabal wind temple there. The stones are all pillars about twice the size of the player with two flags on them.

• Reveal Soul: Mana cost 5, cooldown 5. Reveal the blueish soul orb left by deceased thieves and adventurers. Certain spells must be cast in proximity to a soul.
  
  
• Call to Elements: Mana cost 5, cooldown 120. Grans you a boon that varies according to your location when casting this spell.
  
  
• Weather Tolerance: Increased your hot and cold weather defense by 8. Increases your decay resistance by 5.
  
  
• Mana Push: Mana cost 5, cooldown 15. Spell which inflicts no damage but has high impact in a wide area in front of the caster. Can be combined with other spells for powerful effects.
  
  
• Point Skill - Shamanic Resonance: The effects of boons on you are increased. For example, a boon that increases your fire resistance by 20 would increase by 30 instead.
  
  
• Sigil of Wind: Mana cost 10, cooldown 100. Requires activated wind altar. Create a magic circle on the ground. Certain skills have additional effects when cast within this circle.
  
  
• Infuse Wind: Mana cost 15, cooldown 240. REquires activated wind altar. Increases the impact and attack speed of your melee weapon for 3 minutes. Your stamina burn increases more quickly however.
  
  
• Conjure: Mana cost 10, cooldown 8. Spell which does nothing on its own, but can be combined with other abilities.

Wild Hunter, Berg

• Evasion Shot: Stamina cost 12, cooldown 30. Requires bow. Shoot an arrow while jumping backwards. Causes the Cripple status effect on the target.
  
  
• Enrage: Cooldown 500. Grants the rage boon, which increases the Impact of your attacks. Using this skill burns a bit of your max health until the next time you sleep. Certain skills require this boon to be active.
  
  
• Hunter's Eye: You can lock on enemies at longer distances when using a bow.
  
  
• Sniper Shot: Stamina cost 15, cooldown 30. Requires bow. Let loos a very strong arrow shot with a long windup, making it a poor option in the middle of combat.
  
  
• Point Skill-Survivor's Resilience: Increases your max health by 40.
  
  
• Predator Leap: Stamina cost 13, cooldown 40. Requires rage boon, melee weapon. Jumping attack that creates a shockwave upon landing, with high Impact and Damage. Requires the rage boon.
  
  
• Piercing Shot: Stamina cost 15, cooldwon 30. Requires bow. Strong shot that goes through enemies and hits other foes behind. Inflicts Extreme Bleeding.
  
  
• Feral Strikes: Stamina cost 10, cooldown 8. Requires melee weapon, rage boon. Attack twice, consuming your rage boon in the process. Inflicts extreme bleeding and pain.

Rune Sage, Berg

• Runes: The rune sage has 4 runes you can purchase, each of which is part of rune magic. They all have the following description: mana cost 8, cooldown 2. Requires lexicon. Red rune that does nothing on its own, but can produce combo effects by casting other runes in the correct order.
  
  
• Point Skill - Well of Mana: Increases your max mana by 40
  
  
• Arcane Syntax: Gain access to more advanced runic combos.
  
  
• Internalized Lexicon: Removes the need to have a lexicon in your off hand to cast runes
  
  
• Runic Prefix: All runic spells are more powerful or have added effects

Lavat's trainers deal mostly with movement and using equipment, they would be very good for anybody who wants to flip around and run like sonic.

• Mercenary, right outside the palace. Deals with armor, equipment and the pistol.
  
  
• Shatter Bullet: 5 Second Cooldown, requires pistol, iron scraps. "Load a bullet with high Impact, which also inflicts Pain. Shooting it requires the use of the Fire/Reload skill"
  
  
• Frost Bullet: Requires pistol, cool boon. Load the pistol with a bullet that makes a short-distance blast which slows enemies. Removes your Cool boon. Shooting it requires the use of the Fire/Reload skill.
  
  
• Fast Maintenance: You repair your equipment 50% faster when you allocate time to Repairing in the rest menu.
  
  
• Armor Training: Decreases the stamina and movement penalties from wearing armor by 50%.
  
  
• Point Skill -Swift Foot: Your movement speed is creased by 10%
  
  
• Marathoner: Sprinting consumes 40% less stamina. cost 600 silver
  
  
• Shield Infusion: Stamina cost 5, cooldown 60. Requires shield. Block an elemental attack. When you next block, an elemental explosion will burst from you. cost 600 silver
  
  
• Blood Bullet: Mana cost 12. Requires pistol, posessed boon. Absorb the enmies life into your pistol as a blood bullet, healing yourself. Shooting it requires the use of the Fire/Reload skill.

Rogue Engineer, Slums. Deals with daggers and movement.

• Backstab: Stamina cost 5, cooldown 15. Requires dagger. Dagger attack. If the attack hits the enemies back, the damage and impact are tripled.
  
  
• Opportunist Stab. Stamina cost 5, cooldown 10. Requires dagger. Dagger attack. If the enemy has the pain or confusion hex, this attack's damage and knockback are doubled. If it has both, they are quadrupled instead.
  
  
• Sweep kick: stamina cost 12, cooldown 15. Weak attack with a wide arc of effect and high Impact. Will knock down a target afflicted by the Confusion status effect.
  
  
• Pressure Plate Training: Enables you to deploy the complex pressure place traps. These traps are primarily armed with charges, which shoot poison, fire and more.
  
  
• Point Skill - Feather Dodge: Lowers the stamina cost of dodging by 50% and allows you to dodge unimpeded even when wearing a backpack.
  
  
• Serpent's Parry: Stamina Cost 7, cooldown 100. Requires dagger. Counter a physical attack with a strong dagger strike. Targets afflicted by confusion are briefly stunned. Targets afflicted by pain will be inflicted with extreme bleeding.
  
  
• Stealth Training: Enemies will have a harder time spotting you. Sprinting and having a light source will still easily alert them though.
  
  
• Pressure Plate Expertise: Increases the power of your pressure plate traps. Allows the reuse of pressure plates after they have been triggered, though they must be re-armed with another charge or compatible item.

Warrior Monk

• Focus: Cooldown 500. Grants the Discipline boon, which increases the physical damage of your attacks. Using this skills burns a bit of your maximum stamina until the next time you sleep. Certain skills require this boon to be active.
  
  
• Brace: Cooldown 200. Blocks an attack, restoring your stability and giving you the discipline boon. All nearby enemies are knocked back.
  
  
• Slow Metabolism: It takes more time for you to become hungry, thirsty and sleepy.
  
  
• Point Skill - Steadfast Ascetic. Increases your max stamina by 40.
  
  
• Perfect Strike: Stamina cost 10, cooldown 30. Requires any melee weapon, Discipline boon. Lunging attack that ignores all defenses and inflicts pain.
  
  
• Master of Motion: While under the effect of the discipline boon, imapct resistance and all damage resistances are increased by 15.
  
  
• Flash Onslaught: Stamina cost 25, cooldown 240. Requires melee weapon, discipline boon. Attack all enemies within a close distance with increased damage and impact. Using the skill consumes the discipline boon.
  
  
• Counterstrike: Stamina cost 12, cooldown 100. Requires melee weapon. Completely block a physical attack, striking the attacker and delaing high damage.

Philosopher (Chakram)

• Chakram Pierce: Mana cost 5, cooldown 6. Requires chakram, discipline boon. Launch the disc forward, possibly hitting the enemy twice. Discipline is required to cast this spell.
  
  
• Chakram Arc: Mana cost 8, cooldown 12. Requires Chakram, Discipline boon. The disc sweepts the area in front of the caster, dealing high damage and impact. Discipline is required to cast this spell.
  
  
• Sigil of Fire: Mana cost 7. Consumes fire stone. Create a magic circle on the ground. Certain skills ahve additional effects when cast within this circle.
  
  
• Mana Ward: Mana cost 7, cooldown 20. Envelops you in mana and, for an isntant, you become immune to damage. CAn be combined with other spells for powerful effects.
  
  
• Point Skill - Leyline Conection: You regain .15 mana per second. This is a constant effect.
  
  
• Chakram Dance: Mana cost 20, cooldwon 120. Requires chakram, discipline boon. The disc sways left and right as it advances, hitting multiple times and dealing high damage. Discipline is required to cast this spell.
  
  
• Sigil of Ice: Mana cost 7. Consumes cold stone. Create a magic circle on the ground. Certain skills have additional effects when cast within this circle.
  
  
• Fire Affinity: Increase your resitance to fire by 20 and the fire damage you inflict is increased by 15%.

There are a few skills you can't learn from trainers. Some, like learning backstab in the prison, can be learned from a trainer at another time. Others, like the various boons and flamethrower, can only be learned from individuals. I'll try and detail these here. When I have time I'll provide more specific information. These skills all cost 50 silver.

The boons all provide bonus resistance and damage, and are found throughout the world.,

Cool - learned from a Watcher in the leyline. Increases ice damage and resistance, and provides heat protection

Posessed Boon - Learned from the Immaculate in Immaculate's cave, which is easily found near the leyline mountain. When he asks what you want, ask for power. improves decay resistance and damage

Warm Boon - Learned from a trainer in Lavant. Increases fire damage and resistance, and provides cold protection.

Blessed - Learned in Monsoon. Increases lightning damage and resistance.

Mist - Learned in Berg in the Blue Chamber. Increases Ethereal damage and resistance

You gain a weapon skill in the beginning of the game based on what weapon you had selected. You can also eventually learn all the skills from various trainers in the game.

Pommel Counter - Claymore - Burac Carillon in Cierzo
Counter an attack with a high impact strike using the sword's pommel. Inflicts Confusion, and can chain into melee attacks.

Talus Cleaver - One handed axe - Oda Kazite in Cierzo
Low blow that reduces the target's mobility. Inflicts Pain, and Cripple.

Mace Infusion - Mace - Taleron in Berg
Block an elemental attack, infusing your weapon with that element.

Execution - two handed axe - Sagarn Battle Born
High damage and impact strike that deals twice it's damage to knocked down foes.

Juggernaut - two handed mace - Soeran in Monsoon
Slow but powerful melee attack that inflicts Confusion. Increased impact resistance during this attack.

Moon Swipe - halberd - Wandering Mercanary in Monsoon inn
Double attack that deals high damage, and that increases in power. If you have the “Rage” or “Discipline” boons.

Puncture - one handed sword - Markus in Levant slums
Close combat attack that deals high damage and impact, and inflicts Pain.

Simeon's Gambit - spear - King Simeon in Levant Palace
Deflect a melee attack and counter with a powerful strike. You will still strike even if no attack was deflected, but for less damage.

Here I'll be detailing the various story passives. I can list all the passives here but I'm not 100% on which storyline gives you certain ones as I've only played through the Holy path so far. This section will likely take some time, I'll probably have to go through with the dev console to have the skills to give proper descriptions and names. Or just wait till I play through the entire game and remember to always note them and such.

Holy quest line skills -

The first decision you make with Elatt will be to either take a boon yourself or give it to Ophiele. The first boon gives you a bonus to decay resistance.

The second decision a choice between two perks, one reduces stamina and mana consumption and the other improves your damage.