Deadlift--make sure your form is right or you can hurt your back. One of the most basic and useful exercises in my opinion, picking stuff up off the floor is something you actually do. As a bonus it exercises your back and grip.
Lunges--take a big step forward or a big step back, then return to start.
It's important to work both your quads and your hamstrings, and to stretch. I got this knee pain for a while and I looked it up and it said my quads were tighter than my hamstrings, so I stretched them and did a bunch of hamstring exercises and it went away.
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