My answer is….I dont know. Give me a second and I will explain how you may be able to tell me what you need to do. Rather than give you exercises to do, I will try to give you a more of a systematic way to look at the leg and its functions. In general, I would say myofascial release, stretch and strengthen areas that will influence dysfunction, but please allow me to elaborate.
First of all, your knee itself is kind of like a series of caves that allow ligaments and tendons to connect the muscles bones of the upper and lower leg. The knee is positioned to act as fulcrum, so that the muscles and fascia can create or resist forces. So there really isnt a “knee” exercise, technically speaking. With that being said the knee is subjected (in this case very dramatically and determintally) to the many muscles that attach above and below at either the hip or foot and ankle.
Now to answer your question of what to do. For me, I would look for clues. Knowing that the hip and foot/ankle are culprits for knee problems, I would look there for some visual evidence. Maybe start at the foot and assess for neutral for position and arch type. If your client can’t bear weight, tale a look the foot for any abnormalities such as bunions or lesser toes deviations. This can be used as clue as for how the foot is striking the ground and you could make a link between type ankle and how the pelvis is shaped. You may even look to see if there is a discrepancy between the lengths of the two legs. Looking at the feet, the hips, and the leg lengths you will be able to come up with a plan to release tight fascia, increase the length of tightened muscles, and increase the communication between muscles.
So let’s say you follow my advice, and inspect to determine a flattened foot and anterior pelvic. You could try rolling out the foot, the tibialis anterior and posterior, stretching the soleus and hip flexor. I say that I cant what you should do though, because I think if is important you see for yourself what doesnt look right on their leg and go from there.
hope this helps,