ToME: the Tales of Maj'Eyal

Combat training should be unlocked (or have a method where it can be unlocked) for everyone in arena or the infinite dungeon, as it has skills that may be useful. In campaign you can buy it for 50 gold, but no such luck in the arena.

You can get a potion that unlocks it in the ID. Not sure about arena. Maybe the potion should be added to the shop there.