Where is the Speed sensor located?

Which one? There are speed sensors at each wheel and 2 inside the transmission. What is the issue you have? That would let us narrow down which one is involved. For instance, an ABS problem or the speedometer isn't working or?

Okay, the P0720 is a code for the "revolution sensor" circuit. This is the sensor that is in the rear of the transmission with a cable that runs in the case. It is a circuit code which means it could be the sensor or that the harness to the transmission is damaged. To get to it you drain the transmission fluid out, then remove the driveshaft. Then to get to the sensor you remove the tail shaft housing, and the transmission pan the sensor harness is in there.
However, I would check the harness that runs from the transmission up to the powertrain control module. It would be an open circuit which would be a cut or rubbed through wire. If no damage is found in the harness, then the transmission will need to be opened, and the wiring checked in it. All of the control parts are inside the transmission and the sensor is in series with the shift sensor and the TCM.

If you need more info we will be here. Those can get involved when you start looking for issues.