if you take Skill focus (use magic device) on an improved familiar (specifically a brownie) does it get to use that on wands and other magic-activation items? I know you use your ranks and your familiar's charisma but I wasn't sure if you could use miscellaneous modifiers for the familiar.
However, if YOU have skill focus your familiar does not gain the benefit. The only thing your familiar gets from you is your actual skill ranks - it does not get any other bonuses to skills that you gain from any other source including feats.
Are you saying "if my brownie gets the feat Skill Focus (UMD) somehow, does it work?" or "if I have Skill Focus (UMD), does my brownie get the benefits?"?
If the former, what Blakmane said.
If the latter, no. All it gets are your ranks. It doesn't even get your bonus for being a class skill.