That looks like maybe a piece of shed that didn't come off cleanly. I would try applying some plain aloe to the toe and see if that helps the shed come loose. I would also pick up some plain neosporin in case it does start to open or appear wounded. That may help an open wound heal without getting infected.If the wound starts to travel further up his hand, I would have a vet check on it to halt any infection before it becomes a major issue. Hopefully it's just a stuck shed that will come free with a bit of help.