I have damaged posterior meniscus in both knees, but refused the operation many years ago because I was too young.
I've had to quit playing football because it was too hard on my knees, but I've kept doing TKD all this time.
You'll have to be careful with stretching and have to make sure that none of the normal movements in your training actually hurt you. If any of the movements regularly causes you pain, you'll have to change your technique to work about it. In TKD, we pivot a lot, without planting the foot into the ground. Because of this, there is very little rotational force on the knee, and it's fine. I don't have a problem with locking the kicks either, but you'll have to see how you react.
You'll want to be careful about injuries too. If you sense pain in your knee after a training session, TAKE A FEW DAYS OFF, and it will likely be better after a short break. If you train through it, you will be out of commission for weeks, as you notices, and my experience confirms this. Once I trained through pain for a week because of a demonstration and had severe pain walking for a few weeks. It took 6 weeks to get back to light training. Since then, I'm extra careful. If I feel pain, I'll take a day or two off.
But this rarely happens, and most of the time, it's training at full intensity.
You should also work on strengthening your knee. Stuff like stepping, running upstairs, step-ups, lunges and squats are good for knee stability (if done properly -- squat by sitting bac, and not by bending your knees forward!!!). In general, do exercises for the quads and hamstrings, but avoid shearing forces on the knee and avoid twisting the knee. So no leg extension machine and the like.
Hope this helps. The doctor told me that I'll have to operate, and that I should simply run until it breaks and then go and do the operation. That was 7 years ago, and I'm feeling stronger than ever.
Just know your limits, understand that you are injured, strengthen your legs and learn to live with it, and you'll have no problem.