Now I have read through the thread and I have seen lots of talk of various mechanics. What I haven't seen in any examples of actual knife disarms. My original Martial Art was Jujitsu and I have since studied Aikido and Judo. While not my school the following series of Videos I have found handy for showing my GMs what my character was doing. I do know that some people on this thread have touched on similar techniques but sometimes it's best to have visuals to go with mechanics.
Jujitsu knife Defense