The correct choice is whose. So what is the difference between whose and who's? The word whose is the possessive form of the pronoun who.

Who's and whose are easy to confuse. Who's means who is or who has. Whose shows possession (e. g. , never trust a doctor whose plants have died). Who's is a contraction of who is, as in who's there? And the friend who's calling, or of who has, as in who's got the time? and the friend who's helped before.

And the friend who's calling, or of who has, as in who's got the time? and the friend who's helped before.