How do you tell what level the henchman is? And their stats? The manual sez that when the PC levels, then he can talk to the hireling and you get a 'level up' dialog option. I'm not getting that,,,,any help?

If the henchman is dead, they won't lvl up. If all else fails, remove them from party, and then invite them again, then tell them to lvl up.

You can look at their character sheet by right clicking on their portrait (or them in-game), going to more actions and clicking examine.