Any suggestions on transportation from Trier to Luxembourg City for 3 adults? While in Luxembourg City, we want to visit the American Cemetary. How far from the city center is it, do we need transportation or can we walk? Any other sights in Luxembourg City to recommend? We only have a few hours to spare for this trip.
For travel from Trier to Luxembourg I'd strongly recommend the train - they're about hourly and take around 40-50 minutes. It's a local service and you won't get much discount booking in advance. Looking at maps you can get a bus route 15 from Luxembourg station to Hamm where the cemetary is, but it looks as if it might be a bit of a walk from the bus stop.
You should alight in Cents-Hamm station and walk for around 30 minutes alongside a rather pedestrian-unfriendly road to the cemetery. My suggestions: take a taxi or, wanting to save time, rent a car in Trier and drive straight to the cemetery, which is close and easily accessible from the A1 highway, exit 7.
The "Tagesticket deLux" is a daypass that gives you unlimited travel on the local and regional trains between Trier and Luxemburg - good for the round-trip in other words - for 10.80€ (price-level 2 for this segment.) Buy this daypass at a VRT ticket machine in Trier. The VRT (Trier travel authority) offers this page on the ticket in German: http://www.vrt-info.de/uebergangstarif-luxemburg.php
To answer your question about other things to do in Lux City - the casemates are really cool and the cost to see them is only a few euros. In the Ville Basse (Low City), there's lots of shopping and restaurants. Below is the Lux City tourism website for more information: http://www.lcto.lu/en/index