How long has it been there? Is it raised at all, or just a spot where he has no pigment? If its been there since he was born, it’s probably nothing, just a little birthmark, basically. However, if it’s new or changing, and particularly if it seems to be raised like a little mass, you should probably get it checked out at the vet. Dogs can get mast cell tumors and other things like that on their noses, so it’s def important to make sure it’s not something that needs to be addressed. But if it’s a flat, unchanging white spot in an otherwise healthy young dog, it’s unlikely to be anything too concerning. There are a host of dermatological conditions that can cause depigmentation.