He's playing, but he doesn't know how to play with humans correctly. He's 8 weeks old and only a tiny baby, a complete infant. He knows nothing. He doesn't know that biting hurts humans. That's how he played with his litter mates!
You should scrap the dominance crap. Dominance between dogs and humans isn't a thing and is based on a study of a pack of unrelated wolves in captivity decades ago. Naturally, wolf packs are related and, well, they're not dogs, soo... It has since proven to be a defective study. Mostly, trying to assert dominance over your pup will result in a broken relationship and a dog that is scared of you because he doesn't understand what you want.
Some puppies don't really understand the whole petting thing, and when they see your hand coming at them they think you're going to play. It's easier to pet the pup when they're a little tired and calm. Sometimes you can't really pet them at all until they're older, which is fine.
Teach puppy appropriate play behavior by shoving a toy in their mouth when they try to go for your hand, and then praise him for using the toy. If he continues to want to use your skin, withdraw attention by stepping behind a baby gate, closing a door, or whatever for like ten minutes or so. Whenever puppy teeth meet human flesh, attention should be withdrawn. Eventually, puppy will learn that he shouldn't bite humans for play or the game ends.
This isn't an overnight solution. Most puppies are pretty mouthy for the first 6-9 months of their life, depending on the breed. It is a constant training effort to teach your pup the proper way to behave, so it is important to remain consistent. The mouthiness will slowly decrease, you'll notice improved bite inhibition, as well his impulse control, because they tend to bite more when they get excited!
