When I learned, I had an OS .46FX with a MAS 11x7 which was the best combo for it. I would say any prop ranging from 11x5-7 would be fine. For trainers, speed is not needed. I would probably go with a MAS 11x5 or 6, then try a 11x7 if the motor can turn it. The MAS 11x7 would be a little faster prop than the MAS 11x5 or 6, but with any trainer, throttle control is very important.

Notice I only recommend MAS (Master AirScrew) props. I am a club instructor now and I only use APC props now, but for learning MAS are the best. APC props will break too easily while learning to land. So for training purposes stay with a MAS prop. Will cost less in the end.