Where is the crankshaft position sensor located?
Why are you asking? Are you going to replace it yourself? Do you want to know why it cost so much to replace it? Or curiosity?
I suspect you are not going to replace it yourself because you didn’t tell us what engine is in the car. That matters.
It varies from car to car, but it pretty much has to be somewhere near the crankshaft, which is the near the lowest part of the engine, so usually accessed from under the car. It’s an electrical gadget that produces a signal every time the crankshaft makes one full rotation.