Here’s the cover letter attached to the subpoena, explaining House Judiciary’s rationale for conducting a deposition.  Pomerantz worked on the Trump investigation for the Manhattan DA’s office, resigned in protest when Trump was not charged earlier in DA Bragg’s tenure, and wrote a book about the experience.

I don’t know how much Pomerantz knows about the existing case that isn’t already in the book or otherwise in the public domain, but I wouldn’t be surprised to see a court asked to weigh in on the propriety of the subpoena.