Whose and Who’s

Whose is a question word. It can be used with a noun.

Whose bag is this?
Whose daughter do you think looks the cutest?

Whose can also be used alone.

Whose is this bag?
Whose is that?

Prepositions with whose

In a formal style we put prepositions before whose. In an informal style we use prepositions at the end of the clause.

For whose benefit is this? (Formal)
Whose benefit is this for? (Less formal)

On whose side are you? (Formal)
Whose side are you on? (Less formal)

In short questions which have no verb, prepositions can only come before whose.

‘I am going to buy an apartment.’ ‘With whose money?’ (NOT Whose money with?)

Whose and who’s

Whose is a possessive word. It means ‘of whom/which’. Whose is used in questions and relative clauses.

Whose is that car? (NOT Who’s is that car?)
The boy, in whose pool we swam, is very tall.

Who’s is the contraction of who is or who has.

Who’s that? (= Who is that?)
Do you know anybody who’s working in an insurance company? (… who is working in an insurance company.)
I have got a cousin who’s never seen a movie. (NOT I have a cousin whose has never seen a movie.)