The 'CJ' Tech in Dead by Daylight is when a survivor performs an action as the killer goes to press 'space bar' whilst another survivor is downed near the killer. This forces the killer to pick up the downed survivor involuntarily. Most commonly used to force the killer into picking up someone with decisive strike, or to allow a potential flashlight save.
A common scenario where a The 'CJ' Tech would be applied is when a survivor is dowed near a pallet. 'Crawl to the pallet, imma CJ this fool' - Squoosee. Stunning the killer then vaulting into them as they go to break the pallet will force a pick up animation allowing for potential flashlight saves.
In the game "Dead by Daylight", a player by the name of CJ created a tech, and thus it had been named after him.
To preform a CJ Tech, you need: a pallet, a slugged teammate, and a flashlight. Make sure your teammate is on the side of the pallet that the killer is on, then once the killer tries to kick the pallet, vault it. This will cause them to instead, pick up your teammate, in which case, you can vault back to the other side and get an easy flashlight save.
Search "cj tech" on YouTube to see this visually.
"He's down'd at a pallet, I'm gonna go for the cj tech!"