Is he actually performing the jumping portions? How much pounding/how much pain is he having with the impact? How’s his gait? Does he have full knee extension during swing-thru and with heel strike? Knee stay bent when standing still? Hows the hip strength and ROM?
Ironically, knee pain (and most joint pain) comes from weakness somewhere else, usually in the joint above or below the painful one, unless there was trauma to the joint itself. But even then, over time, it can get worse because of overcompensating.
Strengthening the knee will help the symptoms, maybe short-term. Assess and find his weakness and ROM limitations, probably in the hips and more than likely in the HS, if it’s OA. You’ll do him a greater good in the long run. Would benefit from stretching of the hamstrings and strengthening to the hip external rotators and abductors, in addition to the TKE’s.