If interviewer asks you this question "  Tell me sth about you that’s not on the application or resume " , what do you want to talk about?

Do you think it is a good idea to talk about my hobbies?

Thanks.

In my opinion, you can talk about anything you want the adcom know, e.g. you can talk about some experience in your life which have forged your character, or your family member which gave you most significant influence.  Conclusively, any story can support your candidacy before the adcom.

Usually, there would be a question about you hobbies.  So do not waste the question on this.   

Just my 2 cent

talk about your extracurricular activities

or your interests and hobbies

LZ's question is good...

what shall I talk about? Because I cover the hobbies,interest,extracurricular activities on my resume....not good to do that then i don't know what i should talk about if the interviewer ask me that