In what amendment was the subpoena?

The term "subpoena" is not explicitly mentioned in the U.S. Constitution or any specific amendment. However, the right to issue subpoenas is derived from the broader legal principles established by the Constitution, particularly the Sixth Amendment, which guarantees the right to confront witnesses and obtain evidence in criminal cases. Subpoenas are also governed by federal and state laws, which outline the procedures for compelling testimony or the production of documents in legal proceedings.