The camshaft position sensor (CMP sensor) on a 1999 Dodge Dakota 3.9L is located on the
passenger side (right side) of the engine, near the front of the cylinder head. It's usually mounted on the valve cover, but sometimes it might be directly on the cylinder head itself, depending on the specific engine configuration. It's a relatively small sensor with a single wire connector.
Because of slight variations, it's best to consult a repair manual specific to your 1999 Dodge Dakota 3.9L. A visual inspection using a diagram from a repair manual will confirm its exact location on your engine. A Chilton's or Haynes manual will be invaluable.