You can fill in the blank below with the following:
Excellent, Fantastic, Wonderful, Great, Not bad, Good, Fine, Not great, Not good, Terrible.
Pat: How are you (doing)?
Max: ________, thanks, and you?
As for "What's up?", it means "What's new with you?", so the response is variable. A standard reply is, Not much (is new with me). What about you?
Student or Learner