Anyone can tell me a true difference between WHO and WHOSE?

WHO in a question basically means "Which person."

e.g.

My door is fixed. Who fixed it for me, so I can thank them?

WHO as a relative pronoun is used to specifically say which person or people we are talking about.

e.g.

Out of these five students, Khadeejah is the student who scored a full mark.

WHOSE in a question refers to "which person whom something or things belongs to."

e.g.

Whose keys are those? = Which person whom the keys belongs to?

WHOSE as a relative pronoun is used to specifically say which person or people possess something or things.

e.g.

I am the person whose wallet was missing. Thank you for keeping it.