A155
2d10
Monk unarmed damage does not progress beyond 20 by RAW

Non-RAW you could houserule by continuing the pattern.
20-23: 2d10
24-27: 4d6 (since you go from 1d10 to 2d6 at 12th)
28-31: 4d8
32-35: 4d10
36-39: 8d6 (now it just gets weird)