The third bail jumper is a man named Glenn Scoville, and his location will be on top of Mount Chiliad. Instead of driving to the top or flying there, use the cable car at the base to get to the top, as this will be close to Glenn's location. When you get to the top with the cable car, grab the nearby parachute if needed, as you will be needing it very soon.
Go behind the cable car station and then south, along the western ledge of the mountain, until you spot two people talking. Once is Glenn and the other is his friend, but as soon as you get close enough, Glenn will jump off and open his parachute. Follow suit, noting that there's another parachute on the ground next to the bike, and do the same as Glenn.
If you try hard enough, you can land and take down Glenn without touching the ground, but that would be challenging and isn't needed at all (there's no challenges for any of these bail jumpers). Land and give chase after Glenn, where he will surrender at the slightest bump. Bring him back to Maude's place to finish the mission.