Make sure the console is enabled. If not, go into Options > Keyboard and scroll down until you see "Developer Console" and enable it.

Here is the command itself:
vocalize <EventID>

You should replace <EventID> with the ID's below

Command Wheel

• CommandYes
  
• CommandNo
  
• CommandZombies
  
• CommandFollow
  
• CommandThanks
  
• CommandStop
  
• CommandBarricade
  
• CommandHelp
  
• CommandNeedWeapon
  
• CommandNeedAmmo
  
• CommandNeedHealth
  
• CommandTakeThis
  
• CommandCoverMe
  
• CommandLetsGo
  
• CommandNoProblem
  
• CommandIllFollow

Auto Commands

• AutoFoundWeapon
  
• AutoFoundItem
  
• AutoFoundAmmo
  
• AutoFoundBoltcutter
  
• AutoFoundFireExtinguisher
  
• AutoFoundNailgun
  
• AutoFoundKeyCard
  
• AutoFoundKey
  
• AutoFoundHealth
  
• AutoBreakable
  
• AutoFoundSurvivor
  
• AutoIdle
  
• AutoDoorLocked
  
• AutoDoorClose
  
• AutoHeIsInfected
  
• AutoSheIsInfected

Events

• CommandJoinTeam
  
• EventFriendlyFire
  
• EventGrenade
  
• EventExtractionPoint
  
• EventInfectedHe
  
• EventInfectedShe
  
• EventTurning
  
• EventPain
  
• EventDrown
  
• EventTaunt

Secret Events

• Auto (only works when looking at ammo and weapons)
  
• CommandJoinTeam
  
• SurvivorDeath
  
• SurvivorPain
  
• SurvivorAttacked