Yes, you can file RTI on someone else's behalf, but you cannot keep your identity anonymous.

Yes, you can.
Under the Right to Information (RTI) Act, 2005, there is no restriction on who can file the application on behalf of someone else—as long as the applicant is an Indian citizen. You can:
File an RTI for information concerning another person (e.g., family, friend, colleague).
Mention in the application that you are filing on their behalf (if you wish), or keep it general.