Is there a way to learn what my secondary hand unarmed damage actually is? I have tried viewing my characters in the Cosmic Forge editor but it tells me that my level 20 monk with 18 str has only 2-4 damage (screenshot attached) which I don't believe is true (he does more damage in fights). I just can't decide if it's better to leave the secondary hand of a monk/ninja character empty or to equip it with some weapon.

The Monk's and Ninja's secondary hand unarmed should count as weapon which does 2-8 damage (+str bonus) with a 5% Bonus on critical hits. In my game both monk and ninja didn't bother with weapons, the Sai is the best secondary hand weapon for Ninjas (or maybe nunchaka because it has bash as standard attack type), does a little more damage but blocks an inventory slot.

I have found an interesting modification called Weapon Equip in the CF editor. According to its description it seems the game really gives you only 2-4 damage for secondary hand unarmed (no Hands&feet skill bonus, no STR bonus, no Critical chance). So you can have 20 STR, 100 Hands&feet, 100 Kirijutsu and you still get only 2-4 damage for your secondary hand without the possibility to hit critically. This mod is supposed to fix this giving you almost the same damage as primary hand and the same critical chance so I think I will give it a try.

Strange. I'm quite sure I would have noted my Monk and Ninja doing only 2-4 damage constantly with their punches (always had them kick as primary attack).
Try out in the game if this is really so, I strongly doubt it.

It is so for the secondary attack. The primary attack is fine.
They've fixed this bug in Wizardry 7.