Which action should be taken to check the parking brake function?

To check the parking brake function, pumping the brakes to reduce air pressure is crucial because it helps ascertain whether the parking brake can hold the vehicle in place effectively. This action simulates conditions where the brake system operates under lower pressure, which can reveal if the brake is functioning properly or if there are any underlying issues, such as air leakage or brake wear.

By reducing air pressure, the driver can observe how well the parking brake engages and holds the vehicle stationary, ensuring it's capable of doing so during typical use. In contrast, while other options like turning off the engine may be part of general vehicle operations, they do not specifically serve the purpose of assessing the parking brake's performance. Engaging the accelerator or depressing the clutch could inadvertently affect the vehicle's ability to remain stationary, providing no insight into the parking brake's capabilities. Thus, pumping the brakes is the appropriate action to evaluate the parking brake effectively.