The Enterprise Incident - S3-E2
Corrected entry: The Romulan Commander believes that Spock is trying to steal the cloaking device. So she hauls him down to the room holding it, goes into the room, and looks pretty much everywhere except the spot where it was mounted - doesn't she know where the device is. Finally her sub-commander tells her that it's gone, and she turns around and sees the empty slot.
Correction: She's not an engineer, and quite obviously has no idea how the cloaking device works nor what it looks like. Most people have no idea how their car runs, and it makes sense for the commander of the vessel to simply know what happens, not how it happens.