Final answer:
You should put your hand at the bottom of the steering wheel when backing up with a trailer, making it easier to steer the trailer in the desired direction by moving your hand in the direction you want the trailer to go.
Step-by-step explanation:
When backing up with a trailer, you should put your hand at the bottom of the steering wheel. This position allows you to move your hand in the direction you want the trailer to go, which is more intuitive since the trailer moves in the opposite direction to the vehicle when you turn the steering wheel while reversing. For instance, if you want the trailer to go to the left, you would move your hand (and thus the bottom of the steering wheel) to the left, which would push the trailer in that direction.