Is it okay to ask a professor if he is going to attend a certain conference I am planning to attend a prestigious conference in the near future, and I was wondering if a certain professor who I wish to meet and I would love to do my phd degree and research under his supervision will be attending this conference. So is it appropriate to ask him (by email) if he plans to attend or participate in this specific conference? Or are there other ways to know this information?

P.S. My research interests are an exact match to his research interests.
My two favourite techniques for stalking potential business contacts (including professors):


Email them asking questions about their work.  Once you've built up a bit of rapport, then you can move on to asking about meeting in person.
Check conference programmes to see if they are giving a talk/seminar/poster, and visit them in person then.