WORDS, WORDS, WORDS: Whenever an opposing character uses Outwit, Perplex or Probability Control, place a Whisper token on this card. Give Ebony Maw a free action and remove a Whisper token to use either Outwit, Perplex or Probability Control until your next turn if he can't already. He may be given this free action up to three times each turn.

If he chose prob, would he still receive the benefit of being able to prob on his turn and opponents turn, or is it a single use of prob?

He can use the power until his text turn. So if you use Prob you can use it both that turn and on your opponent's.

And you can not pull a token off his card on an opponents turn to prob, if you did not do so on your own turn, can you?

It is a free action to remove a token so yeah you can't do this on your opponent's turn.