Tactical Awareness is a gear perk that tags enemies through walls. Knowing where guards stand inside buildings makes stealth and breaching much safer.
Enemies behind walls get tagged, so you can see where they are before you go in. You avoid walking into a room with a guard facing the door.
Wear the Caveira Beret in the head slot. Gear perks are fixed to the piece of clothing that carries them, so you get this one by wearing that piece, not by unlocking it in a menu.
Yes for stealth players. Seeing enemies through walls helps in every outpost and checkpoint.