Right on the heels of its vs. it’s are whose vs. who’s. Let me explain:
Who’s is the contraction for who is or who has. Who’s going to the toga party this Saturday night? (Who is going?) Who’s taken my copy of Julius Caesar? (Who has taken it?)
Whose is a possessive pronoun; it shows ownership. Whose car is parked in the 20-minute spot? (Who does that car belong to?)
As I wrote about it’s vs. its, possessive pronouns do not use apostrophes to show ownership. Only nouns do: Caesar‘s attending the toga party Saturday night.
Got it? Good!