Asaki said:
I imagine all of the training and experiences he's gone through until that point.
Agree, but the thing is that it is pretty explicit in ROTJ that he never saw Yoda since he left him at the end of ESB. ("promise to an old friend", him asking about Vader being is father, Yoda being surprised that Vader told Luke about it, etc...). So everything he learned to be close to the Jedi master level, he learned by myself.