Who knows the difference between who's and whose?

Who knows the difference between who's and whose?  

Who's

Who's is a contraction of who is or, less commonly, who has.

Who's watching TV?
Do you know who's going to speak?
Who's ready to go?
Who's in the kitchen?
Who's this?
Who's already eaten?

Whose

Whose is the possessive of who or, somewhat controversially, which.

Whose book is this?
Do you know whose car this is?
I know a woman whose kids study there.
Whose side are you on?
An idea whose time has come.

  
The Bottom Line

The trouble here is due to the apostrophe, which on 99% of English words indicates possession, but on this one simply indicates a contraction. If you can replace the word with who is or who has, use who's. If not, use whose.  

You can find this lesson and more free English lessons at e Learn English - online language learning with Laura K. Lawless