Student or Learner
I don't think he will do it, won't he?
I don't think he will do it, do I?
Which one is more correct?
The first is incorrect. It should be "I don't think he'll do it, will he?" Your second is grammatically acceptable but unnatural. Why would you ask someone else what you think? You already know what you think.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.