There are different types of enemies in Rainbow Six Extraction and most missions will require you to navigate through them. Making your enemy bioluminescent can help you see their movements through walls, preventing any surprise attacks.
To begin, you have to start a mission first, you do not need to bring any specific tools to make your enemy bioluminescent.
Once you are on the mission, look for any weak or breakable walls in the area. Usually, you can look through wooden walls.
Use your flashlight and shine it on the weak surface or breakable wall. You will see that your enemies will become bioluminescent and you can see their movements through the wall. The enemies will not be alerted until you break the surface or the wall.
You can also shoot at them using guns with silencers to avoid alerting them. Shooting at the enemies using guns like shotguns will immediately alert them and they will try to destroy the surface.
You may also destroy the surface yourself by shooting at the breakable wall.
And that is how you can look at your enemies through walls!