I decided to see just how far the Demo class can get without adding any skill points to individual skills. That is, place all skill points into the class level. I suspect once the lack of CC is painful will be the end of this experiment. Along the way I got Francis' Gun in a drop. This gun has an item Granted Skill (fireball), so I decided it'd be OK to use this since it wasn't a skill point assignment.

But it looks like I can't use it. :( I can't assign it to a hotkey slot because it isn't in the list of available skills when I R+Click a slot. I'm sure there is a game mechanic I've missed that I'm not finding. Can anyone point out what I need to do here?

Unless I remember it wrongly that gun have a proc skill and not an actual skill, you get the fireball effect like 5% of the time you attack instead of the actual spell to use as you see fit.
There are items that give actual skills but they are not as common.

That makes sense. Interesting that the description doesn't say "auto skill" or something. Thanks for the info.