…A light bulb.
Ok, I need some help here. The light went out in our closet, so I took the cover off to change the bulb and see this. WTF?
How do I change this?
hope this helps
Oh, that looks tricky! It seems like the bulb is inside a fixture that’s not easy to open. You might need to unscrew or unclip the whole thing from the ceiling or wall to get to the bulb. Just make sure the power’s off before you start! If it seems too complicated, it’s okay to ask for help from an electrician
Looks like it is glued to the surface.
There might not even be a bulb per se.
Just a little LED node.
If so, probably have to replace the entire thing.
Any part number and/or manufacturer on cover?
I suspect the center circle is an LED bulb that has lost its cover, or had it removed to make it fit in the housing. I have some recessed lights in a bedroom that did that. Try unscrewing the center part. But turn off the power at the breaker, first, in case I’m wrong. Or just at the switch if you trust the rest of your household. 
Also, we’re up to 5 for the joke aspect. 
It’s an LED but I’ve never seen one mounted like that before. Is that a hinge top left or a slot that the lug was pushed into when mounting? Can’t see clearly on that flat image. There are the usual screw slots top right and bottom left but no screws as far as I can see - maybe it was glued in place.
If I had that situation, I’d try rotating it gently first, that’ll let you know if it’s glued in or not. If it doesn’t move you’ll have to get a small flat bladed screwdriver or something and try to (carefully!) lever it out - try starting at that lug bottom right.
If you look at top right, there’s a fuzzy area in that slot, looks like a silicone sealant (is that what you call caulk in the US?) If that was used to seal it in you’re going to struggle to get it out without destroying it.
Please, let us know what you’ve learned… or, maybe, you are still in the dark? 
Hope you figured it out!