What must a trainer do before working a horse on the steward's list?

A trainer must contact the clockers before working a horse on the steward's list because clockers are responsible for officially timing workouts and providing documentation of performance for the racing commission. The presence of a clocker is essential during such workouts to ensure the workout is recorded accurately and complies with any specific regulations associated with horses on the steward's list. This practice ensures transparency and integrity in the racing process, allowing for proper monitoring of the horse's performance and condition following any restrictions due to prior issues.

Other options, while relevant in some contexts, do not serve the same primary purpose of documenting and timing the workout, which is crucial for compliance and regulatory oversight.