Basically, connect the o-scope to the knock sensor and tap on the block. You should see a frequency wave on the scope.
It's a very simple test that should only take a couple minutes to complete.
Edit: I just tried testing a knock sensor from a MKIII Supra with a crappy old Wal-Mart special DVOM. I set it to the lowest voltage setting and touched the negative probe to the sensor's threads, and the positive probe to the signal connector. It showed a static voltage reading of around 20mV. When I tapped the sensor with a padlock I had laying around, that reading jumped to about 35mV, then settled back down to 20mV again. It's not the proper way, but if you don't have access to an oscilloscope I suppose it will work.
Oh, and one last thing, there should be no continuity between the ground and signal ends, obviously.
Last edited by shaeff; 10-13-2010 at 06:09 PM.