so we get this question every day. the problem is there are just too many apps to be able to identify just by the notification icon....unless it is something popular like facebook or youtube.
the easiest way is to look at the phones notification bar. but this is not your phone, so that is out of the question. why not just ask?
anyways, since there are too many apps out there, the best you are going to get from us are guesses. but who knows you might get lucky and someone here might be able to recognize it. but, i would not hold your breath for too long waiting for an answer.