It is down under the bottom and kind of hard to get to , but not a big problem. I had my bike torn apart to replace the main wire harness because the wire going to the knock sensor was severed. Thus, I cannot give you a step by step, but I don't think it should be too hard to change out if that is indeed the problem.
The wire that goes to it is part of the main harness and is a shielded cable. Before I replaced it, I would sure try to make sure the wire is still plugged in to the sensor. The "top" end is wired right into the main harness, so the only connection to easily check is the bottom plug.
This is a picture of the plug (broken). [ATTACH=CONFIG]50525[/ATTACH]
This is how it looked up on the front end when I did the replacement-you will not need to disassemble this much though. [ATTACH=CONFIG]50526[/ATTACH]