You will eventually receive a phone call from Dom - the bloke who really enjoys adventure Parachuting - that will come at some point after you have spoken to Lester.
Dom will remind you of the joys of Parachuting, and then he will unlock the various selection of Parachuting Events all around the map. Note that like other events these are Rank based, so the higher your Rank, the more events you will have access to.
The Parachuting Jobs are detailed under the Sports Activities.