If you bought it as a round trip, no. There are indirect ways, though. You can try refaring one leg of the trip using the current fares. If a fare you choose ultimately does not change the total points required to complete the transaction, you know that's the amount of points that leg cost when you originally booked.

As to canceling just one leg, I don't believe you can do that yourself on-line. You'd need to call. As stated just now in another thread, if you do that, you won't be able to make further changes on-line.

My advice would be to perform the steps I mentioned above and if the return flight is still the same fare as when you originally booked, book that as a new one-way reservation in points, then cancel the original RT.