Ailie Baumann is drawing a cartoon Game Ranger and has asked me how to draw knees. Here is a video that I hope will help.
One thing to remember is that people are not viewing your work to criticise the way you draw knees. Whatever you do they will look weird because knees are weird! Make is as simple as possible to make it easy for yourself. The viewer is busy looking at the characters face and what their hands are doing. Their brain will fill in the knee detail. If you over accentuate the knee, then they will notice!
Keep knees simple.
You will find the index for how to draw cartoon people here: shooraynerdrawing.com/ ?