I have a 8 week puppy , and I was giving him a bath today and I think he has fleas,what would be the best thing to use on him.

I think at 8 weeks, you can use any of the modern, effective products. I know you can use the Revolution I use. Best thing is to talk it over with the vet. If you haven't had him long, and winter has set in where you are, you might get away with a spray such as the Ovitrol I have used in the past. Vacuum good discarding the bag. Then spray the puppy and the whole house. Spray again at any sign of fleas. If you haven't had fleas in the house and you wipe out the ones you have and the eggs they laid, you may be good for the winter. I have gone years doing little or nothing. I only started using Revolution because we now have an older dog with a flea allergy in our care.

For more about puppies, see https://www.askmehelpdesk.com/dogs/information-articles-our-dogs-expert-labman-53153.html#post251802

My 7 week old puppy has fleas , what can I do?

I moved your question here because I think my above answer covers your question too. Once they are 6 weeks old, you have a number of good options.