imgur.com/a/E25Iu
I'm thinking maybe a possible burn?I don't have any heat rocks, 4x2x2 enclosure reptisun 3 feet,zoomed basking light,crickets and Phoenix worms,kale,collard greens and bell pepper??
I'm not sure that it's a burn. It looks like a fungus or growth of some sort. If you can get him to a reptile vet I would suggest doing that to have it tested.