I would say "on".
Student or Learner
I know you say be/go on holiday/vacation. But which preposition is correct if I want to express the following:
In my next holiday I'd like to learn how to dive. Is IN possible here? Or would you still say ON?
So IN my next holiday I'd like to .... would never be used?
Not in AmE. "On my next vacation" or "during my next vacation" are possible.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.