To be certain, you should:
* Consult a repair manual: A Haynes or Chilton manual specific to your 1992 Buick Riviera will have diagrams showing the exact location.
* Use an online parts diagram: Many auto parts websites (like AutoZone, Advance Auto Parts, etc.) allow you to select your vehicle's year, make, and model and view a parts diagram. Look for the diagram related to the engine and locate the CMP sensor.
Without knowing the precise engine code, I can only give a general location. Using a repair manual or online parts diagram is crucial for accurate identification.