Hello Natalia, You have two options 1. Qui est ta plus grande inspiration ? 2. Qui est votre plus grande inspiration ? Both literally translate to - Who is your biggest inspiration ? You would use the second option to show respect towards an individual such as an elder. However, it is still common to hear the first option even in such a scenario. I should point out that "inspiration" is feminine. Thus, you cannot use "ton" in this case. Good luck with your studying !

Qui est votre plus grande inspiration ?

On pourra aussi dire "Qui (ou quelle) est ta / votre plus grande source d'inspiration ?"