Long story short, I have to begin retraining the employee who is my backup. Starting tomorrow, he is to shadow me whenever I am doing a task that he may be unfamiliar with. He's gone through training once, didn't take appropriate notes or pay attention, claimed he had no questions, and then panicked when I took two days off. Supervisor asked him what happened and he claimed he hadn't been trained for the situations that came up. (I did not train him the first time, but was nearby. Trainer went over everything.)
How do I politely ask him to take notes so that this issue doesn't arise again?