What are some good physical therapy exercises to do for a torn meniscus?

Many. Physical therapy and rehab exercises for tears of the meniscus will vary based on the severity of the injury, so check with your physical therapist or doctor for specifics. In general, any exercise that strengthens the quadriceps, hamstrings, calves and hips will be beneficial, as will ones that improve balance (proprioceptive exercises), flexibility, and range of motion.
None. While you can do exercises to strengthen the muscles that support and surround your knee, these will not lead to healing of torn cartilage/meniscus. Avoid high impact and twisting/pivoting activities. Best option is to fix the torn meniscus surgically.