L knee gave out jumping rope. the pain (4-10) on the outside of my knee, sometimes behind it. it is unstable keeps threatening to give out again. kneeling, going up/ down stairs, squatting most pain. what parts of the knee could be injured? c doc?

The injury you described could lead to a lateral collateral ligament strain/tear or possibly a lateral meniscus (cartilage) tear, either of which could cause pain when using stairs/bending knee. Depending on severity, you may do fine with rest from stressful-to-the-knee activities & physical therapy to strength the quadriceps, but best to have an evaluation by an orthopedic specialist.