I looked in my tank a couple of days ago and noticed my GT had a small injury to his head. I looked in today and it has gotten bigger. I was wondering if it is "hole in the head", or has he/she just gotten their butt kicked?
It looks like damage from hitting the decorations. But hard to tell from the small pics. What are the tankmates? Something could be chasing or scaring it, causing it to dart into objects in the tank.
A teaspoon per gallon of salt will help keep the wound from getting infected. Keep water clean and remove suspected abrasive decors. Keep then fish isolated to prevent other tankmates from picking on the wounds.