who's, whose

This is an easy one. 'Who's' is a contraction of 'who is.' 'Whose' is the possessive form of 'who.' If you can substitute 'who is' then the word is 'who's.' All other cases take 'whose.'

Who's Boba Fett taking to the Bounty Hunters' Ball?

Whose thermite grenade is this? C'mon, Boskk. I told you not to leave this with the coat check girl.