You need to load the connective tissue sufficiently to promote strengthening, but not so much to cause further injury. The exact exercises you should do depends on what you can handle at the moment with regards to pain. If anything causes an intense sharp pain, that's your body telling you it's causing more damage.
I'm not a doctor, but this is what I would do, and have done with patellar tendinopathy in the past...
Are you able to do squats and lunges? Because if you can do those without pain, gradually increasing the weight you can handle with good control will improve leg and joint strength. If those are too painful then you can start with easier stuff like stepping up and down from a low box, slowly and under control, to help build up your tendon strength. Or if you're going to the gym, you can use the leg extension machine with a very light weight, and use the leg with the bad knee to slowly lift the weight, and slowly lower it. It's important, especially when dealing with an injury, that everything is done under full control, with no jerking of the weight, or fast dropping of the weight.