Hard Bump on Dog's Nose

You did not say whether it is bothering your dog, secreting liquid, or how old the dog is. The worst case scenario is that it could be cancerous, so I would play it safe and call the vet.

In Tahiti this happens quite often when a centipede bites a dog. It can form a hard lump in the area that was bitten. The vet normally gives the dog a shot to reduce the swelling. Anyhow, something has bitten the dog and you need to determine what has. I would take the dog to the vet and have them examine the dog. Hopefully they can drain the area and it will be fine.

It could be a bite or something more serious. You won't be able to tell if he's not showing signs of itchiness or anything. Best take him to the vet.

I hope your dog is doing okay and having no serious problem. If your dog still has the bump on his nose and has not seen a vet I have a suggestion - one that I have used when faced with a similar problem/condition.
Mix about 1/2 cup of Epsom Salt in a pint (2 cups) of hot water. Cool the water until you are able to place your hand in it as you will need it as hot as possible but his nose will be tender so cool it down some. Dip a clean washcloth in mixture, wring slightly, and place on his nose. Hold it on until it cools. Do this several times and it will reduce the swelling and draw any poison (if present) to the surface. Use clean cloths and hot (tested) water with the Epsom Salt and hold on nose - it will help.