There are no 'must sees', anywhere. If you have a GPS, the quickest route from Cochem to Trier will take you via the A1 highway. About 1.5 hours. We stopped off in Wittach once, for a coffee: not worth it.
Keeping to the Mosel or close to it, the drive is more scenic and there are many places worth stopping off at. A straight drive, without stops, will add about an hour to your travel time. Any stops will obviously cut into your time in Trier.
Main stops, for me, are Beilstein, Zell and Bernkastel-Kues. If you are up for a fairly short but strenuous hike, the steepest vineyard in Europe is between Ediger-Eller and Bremm (Calmont Klettersteig): I've done it three ways, only the one has the trickier short rope and ladder path. There are many paths by the river – a simple hike, park in Bullay and walk to Zell and back. St Aldegund is a pretty little place.
I don't know how long you have in the area. I think Bernkastel-Kues is a much better visit than Trier, as is Saarburg (south of Trier).