@NikolaiHansen17 the correct folder is the folder where you downloaded a game.
For example, you downloaded a game in C:\Users[Username]\Documents\pluto_t6_full_game.
In Plutonium launcher, you have to set that folder in order to launch Black Ops 2.
You'll recognize every game by it's short names, with T4 being WaW, T5 being BO1, T6 being BO2, and IW5 being Modern Warfare 3.