Episode 28, Season 2 - Garland Briggs and Judy
Julie: I think you were asking about the original post. The Major Briggs stuff is in episode 28 of the original series, which is the 21st episode of the 2nd season, and second to last overall. The numbering gets confusing because the Pilot was not numbered, but then will likely be numbered by streaming services now, etc.
The reference to Part 17 was about the scene with Cooper's superimposed face in The Return.