This is a great exercise to build up your traps. You do not need a lot of weight to do this, so leave your ego at the door.
To do a drag row with a trap bar, simply stand up with the trap bar and perform an up row. This is not a large ROM, so don't worry too much about how high you can pull it. But make sure you try to pull it as high as possible and to hold at the top for a second.