Cloak and Dagger spies can be hard to find if you aren't a few specific classes. If you are a pyro, soldier, demoman, or a jarate sniper or mad milk scout, revealing them can be difficult. However, since almost all cloak and dagger spies reside in the general vicinity after hiding, I find that this strategy works best with every class: Simply put yourself in a position as if you are defensless, since they thing they will be able to get an easy backstab, and wait to hear or see them decloak. 2 strategies that I regularly employ are to fake afk and wait to hear the decloak or to conga, if you have said taunt, and stop congaing as soon as you see them reveal themselves. The fake afk way can be pretty good but you must be alert for sounds if they decloak behind you. If you conga then you can look around while in 3rd person mode and jump to stop the conga immediately. After they reveal themselves you should be able to easily kill them with your weapons.

In the comments post your specific strategies for dealing with cloak and dagger spies.