For Basic Information just go to “Collison Overview” on the UnrealDocs.
Keep in mind that you need to check if your pawns “Object Type” is really set to “Pawn” to have it work with your turret actors settings. Maybe the “Object Type” you chose for your turret actor is set to be ignored (or blocked, or what ever your problem is) by your pawn ? If you want to use “OnClicked” or “OnTouchBegin” Events with an actor it has to “Block” “Visibility” and “Simulation Generate Hit Events” needs to be set to “True”