If you hover your pointer over the level of the hero on the unit card, it should tell you the current exp and the exp for next level.
I have no idea what is the cap though.
Yeah, and my guy is stuck at the cap exp at lvl 18 for 3 battles where he gained 2k+ exp each.
So I guess level 18 is the hard cap?
If so, the manual is wrong. Or maybe the amount needed to advance rises dramatically at that point?