What are the best traffic pattern airspeeds in a Cessna 172N?
This is really something you should discuss with your instructor, but if you want some general guidance then this should work:


Downwind: 70kts, 10° flaps
Base: 65kt, 20° flaps
Final: 60kts, 30° flaps


I say "guidance" because you may need to adjust this but it is in line with the POH values that you quoted in your comment and FWIW it's what I would use 'by default' in an unfamiliar C172. Although personally I wouldn't use 40° of flaps unless it's a short-field landing: the aircraft will come down more quickly with them fully extended.

But I'm not an instructor and I don't want to make assumptions about what he's teaching you and why, so you should definitely ask him this question. Ask him what power setting (RPM) he recommends on each leg, too.