Which part of the kingpin should the locking jaws close around?

The locking jaws of a trailer's fifth-wheel coupling mechanism should close around the shank of the kingpin. The shank is the portion of the kingpin that extends downward from the base, allowing the locking mechanism to securely engage and stabilize the connection between the tractor and the trailer. When the jaws appropriately close around the shank, it ensures a safe and reliable attachment, preventing any unintended disconnection while the vehicle is in motion.

Choosing the shank as the correct answer highlights the importance of proper coupling technique in maintaining safety on the road. The other parts mentioned, like the base, tip, and cover, do not provide the necessary structural integrity or security that the shank offers when connected; thus, they would not be suitable choices for the locking jaws of the coupling mechanism.