The knocks sensor has to do with your fuel ignition if there is actually a problem you would notice audible knocking from the engine compartment, pinging from engine under acceleration ,loss of power, irregular RPM , . The sensor threw the code with a p0456 code as well this is an evap system code. Bad gas cap bad purge valve or vent solenoid. but when you get both at once it usually means bad gas. this is one of those cases were wait and see is a good idea. Run through a couple of tanks of fuel .It wouldn't hurt to give it an upgrade to high test . Have your engine light reset after the second tank and see if it returns.you really don't want to replace it if you don't have to and if the code does return deal with the evap system first as this can cause the knock sensor to throw a code. If all else fail and you need to replace the knock sensor it is usually located inside the engine under the intake manifold. Hope this helps