The Accelerated Free Fall (AFF) method of teaching skydiving allows students to make solo jumps in a fewer number of jumps. In most place however, this method requires one or two instructors to physically hold the harness of the student until the ripcord is pulled. As such the number of instructors is at least equal to the number of jumpers.
A testifying witness who asserts their 5th amendment rights against self-incrimination can not do so for individual questions. Therefore it's highly irregular to answer subsequent questions after asserting one's rights.
First-time skydivers do not do a freefall jump from 14,000 feet. In the "old" days, 1st jumps, at least into the early 80s, static line jumps like you see in the old war movies) and then increase altitude doing what are called Dummy Rip Cord Pulls (DRCPS) while still having and instructor jump with you to make sure you pull your dummy rip cord at the proper altitude but your chute is still deployed by a static line. Only once your instructor is satisfied do you start dping freefall jumps. Also most people only want to do one jump, they don't want the whole certification, and those are tandem jumps where you are connected to an experienced jumper who does all the work and you're just a passenger.
Characters imply that, despite being a licensed pilot, Bull might be afraid to jump out of a plane with a parachute. In Hung Out to Dry (2003), Michael Weatherly's Tony DiNozzo was accidentally pushed out of a plane.