Add squats. Its the king of workouts.
When you can do 100 air squats, add weight.
When you can do 100 weighted squats, add more.
Repeat
:)
Discussion
Not sure if my knees could take that. I'm a Capricorn who used to skateboard a d didn't land tricks properly. So I have bad knee pain
Some years ago I injured my knee making a bad movement. After that I stopped training legs waiting for the pain to pass. The most of the pain passed but some latent pain remained. I then started to train legs again and the pain disappeared completely. I suggest you to ask for a medical opinion, but what I want to say is that having strong leg muscles relieve the stress on the knees and sometimes may help with knee issues