Final answer:
The appropriate course of action is to request medical clearance from her physician.
Step-by-step explanation:
The appropriate course of action for the trainer when a client indicates a previous surgery on her left knee is to request medical clearance from her physician (option D). This is important because the trainer needs to be aware of any restrictions or limitations in the client's exercise program. The client's physician can provide information about the previous surgery, any residual issues, and any modifications or precautions that need to be taken into account during the training sessions.