The 12 is normal, you'll always see that. It says the knock sensor is on the side of the engine closest to the firewall. It is almost directly under the middle exhaust port of the exhaust manifold about 2 or 3 inches down. But the sensors themselves are'nt usually an issue, its the wiring. What issues are you having besides the SES light? If it's running fine, I would erase the code and see if it comes back.