What question do you ask to find a possessive noun?

A possessive noun is a noun indicating ownership: Who or what does it belong to?

Example: Jason's bicycle is new.

A possessive noun is a noun indicating possession: Who or what has it?

Example: Lunch is Jane's treat.

A possessive noun is a noun indicating purpose: Who or what is it for?

Example: We're going to the children's playground.

A possessive noun is a noun indicating origin: Who or what does it come from?

Example: I'm a fan of Dicken's stories.