This is him he is a juvenile i have him in a 12x12x18 terrarium i have a full cgd diet for him which i leave in a small water bottle cap in a open place every other night. So any advice would be greatly appreciated.
He doesn't look extremely thin, although a body shot from above would be more helpful. It can often be difficult to tell if food is being eaten, so you can also search for poop (if he's pooping, he's eating). If this is a new gecko you've gotten within the last month, you should be handling/disturbing as little as possible and giving him time to settle in.
I hardly ever actually see my cresties eat. All but one seems to prefer to eat in darkness, after the lights are out.
I make sure to see how full their CGD cup is when I put in, then you can see if it's lower the next day. Even then, it's hard to tell with light eaters, especially babies. Look for poo, that's the only guarantee they are eating. No eat = no poop