A shadow exercise was an opportunity for junior officers, especially those in the Starfleet Command Training Program, to build rapport with a bridge officer and learn about their duties and command operations.
In 2257, the USS Discovery's class of CTP trainees, under the direction of Commander Saru, had shadow exercises with the bridge officers after completing a half marathon. While Ensign Sylvia Tilly discussed running a checklist protocol from the Captain's chair with Captain Christopher Pike, Albert Kim met with helmsman Keyla Detmer and operations officer Joann Owosekun, and Andre Haynes spoke with the bridge science officers including Saru and Linus. (DIS: "Point of Light")
The fourth CTP Trainee that participated in the half marathon is later absent from shadow exercises on the bridge.