High Quality Content by WIKIPEDIA articles! A Doe subpoena is a subpoena that seeks the identity of an unknown defendant to a lawsuit. Most jurisdictions permit a plaintiff who does not yet know a defendant`s identity to file suit against John Doe and then use the tools of the discovery process to seek the defendant`s true name. A Doe subpoena is often served on an online service provider or ISP for the purpose of identifying the author of an anonymous post.