Hi in case anyone is still searching for the knock sensor, I recently changed the knock sensor on an FSI I bought. In my case the wiring connector was completely missing when I eventually found the knock sensor. Any way if you are looking for the knock sensor you will need to get it from under the car. I could see no way to access it from above. You will also need to remove the plastic cover under the engine. I jacked and propped the car on stands then was working on my back.
the bolt securing the knock sensor has a 13mm head and is only just visible from an awkward angle, accessing it with a standard socket and extension bar was tricky, for me very tricky. I found that using the video on my mobile to look for the bolt head helped. here are a couple of photos to help you locate the sensor
. Look for the black metal bracket in the photos, the sensor is behind there. When I removed it eventually there was some corrosion on the block. I cleaned it up and the sensor face and rewired the connector (i will post the connector type later as this was quite hard to find out too). Replacing the sensor was extremely awkward - some guidance on the correct tool to use might help others as there must be an easier way than I did it with an extension bar.
the sensor clean up and rewire solved the 16711, 17733,4,5,6 fault codes and the car runs MUCH better now.
thanks to all the other posters, i wouldn't have tried without the previous guidance.