My speedometer isnt working If there is a sensor where is it located Pls explain

have the cluster tested by a mech with a tech2 scanner and have a gauge sweep done to test gauges

It has a speed sensor typically on the transmission that sends a signal to PCM computer and instrument cluster. Generaly we use a scan tool to see if speed sensor is sending a signal. Could be a bad sensor, problem with wiring, PCM, and most often a failed instrument cluster.