Knock sensors can be a pain to get to (located under the intake manifold) combined with being fairly cheap, it would be better just to put a new one on by the time you get to it. If you have a code...
Yes, but it takes a special test module that isn't cheap. Go to a good mechanic and have them test it. It doesn't take long and in the long-run it's cheaper that buying a tool that you may never use...
A sensor is used to measure data from the environment and is able to convert them into signals to be communicated with a system. Most sensors are used to measure light, temperature, touch, sound,...