Where is the throttle position sensor located?

With the engine off, have a friend press down on the accelerator pedal and let it up a few times while you watch under the hood.

You'll typically need to remove some of the air filter and intake hoses to watch the throttle cable function, but note where the throttle opens and closes as your friend presses on the pedal.

The shaft that goes through the butterfly AND THE BUTTERFLY valve are called the throttle. The sensor will be connected to one end of that shaft or the other, and there will be a wire that leads to the computer. All vehicle manufacturers have their own way of doing things, you have to figure out what's going on in YOUR vehicle.
The throttle position sensor is usually located on the end of the throttle shaft on the opposite side of the throttle cable.