Who’s or Whose?
Your choice!
Who's
Exemple : ‘’Who's already finished?’’
The use of the words "who's" and "whose" is often unclear. "Who's" is a contraction of the phrases "who is" and "who has". It has no other uses and should only be used if it can be expanded to "who is/has."
Whose
Exemple : ‘’I don't know whose bag that is.’’
"Whose" is the possessive of "who", or sometimes of "which". It is used to denote ownership most commonly by a living being but also sometimes by an inanimate object.