You want to do a subpoena duces tecum, not a deposition subpoena. The duces tecum is for a production of documents, whereas the deposition subpoena is for the production or showing of documents.
You can obtain a return transcript for the tax year in question. This transcript will show you what was reported on your return. You can also request a photocopy of the return itself, but this requires you to fill out a Form 4506, although it can take a few weeks for this form to be processed and for the return to be sent to you. Ordering the return transcript online or having it mailed to you is much quicker.
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