1:when you reach the 2nd section of the cave head right pick up the shotgun turn left & fight him
use the shotgun or a grenade when he is covered in bees.

2:when fighting the fear of course you can't see him
when you are in the factory where you get too sokolov(not during vartouis mission)in the room where sokolov was held there is a locker open it & there you will find the terminal goggles use it to see the fear even when he is in camo.

3:after you defeat the pain you walk a river when you are in the end of the river turn left.there will be two soldiers take them out get on the platform...