Which 3 skills has your DK learned?
If you save first, can you have your DK learn a skill that you know shows up fine for your hero, and see if that works? Reload afterwards, if you don't want your DK to keep that skill.
IIRC with potions you can just use the function keys. I went into the game options to change some of the default hotkeys; F1-F5 are assigned to character selection functions, and can be changed to free up the function keys for potions and skills.
