Trying to install Cooper surface LED down light to ceiling but don't see a ground wire
If you look inside the box, there is a raised hump with a tapped hole for a ground screw.


Since it looks like your ceiling box is wired with armored cable, the box has no ground conductor as the armor around the cable is the ground conductor. The screw size is 10-32 and you can find packs of green grounding screws at home improvement centers.