I had ITBS/runners knee/jumpers knee many years ago. I also had stabbing pains and my knee would just randomly give out, didn't matter if I was running or walking or just standing around.

If this is indeed your problem, yes to all the above -- foam roller, any IT stretches you can find (you can do this standing up or lying down on your side, like on the edge of a bed or couch), and ice. In my case I also have a tendency for my patella to track improperly (chondramalacia) so I was also told to do exercises to strengthen the inner quads.

I've recently discovered Yamuna body rolling which uses a ball instead of a roller, and I get good results without it being as excruciatingly painful as the foam roller.

Oh, and I just re-read your original post and you said this happened when you were kneeling? You may want to google knee bursitis as well. I don't have personal experience with it, but I remember it coming up in my research when I used to obsess about knee pain.