I would use "What/how did you score on your exam"?
Student or Learner
What/ how much percentage did you get in your exam?
Often I get confused about these words.
Use 'What percentage ...'
Or What mark in British English.
How much percentagedoesn't work.
It would depend on the scoring system for me. If marks are given in percentages, I would ask "What percentage did you get ...?" or "What score did you get ...?" If marking is done using a grading system (A, B, C etc), I would ask "What mark ...?" or "What grade ...?"
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.