jeNYC said:
What is the name of your state?NY
What is the purpose of the supporting deposition? Am I supposed to fill it out and mail it back with my not guilty plea?
The purpose is to give you general information behind the offense you were charged with, such as the weather, traffic conditions and/or the circumstances under which the officer's observation was made. It is so that you can (attempt to) prepare a defense.
You don't need to mail it "back", it's for you.