Engine knocking.. but tech replace knock sensor. If their obd scanner shows no knocking, then yeah they can suspect the knock sensor.

After change still got knock, so they 'tune' the car. Most probably just reset ecu. But still same problem but obd scanner did not pick it up.

Problems still there so they refer to proton.

Could be wiring issue or mechanical knock which out of the frequency range that can be detected by the knock sensor. Either way it seems bad