just go into the dungeon. look at your minimap for an red dot.
if you want to find him quick.
you could use the savedgame editor. here you can put some extra skillpoints in elven sight too find the dragonrider easier.
after you found him you can put these skill point off again!
here's a link:
.2.0b-MinDepend.zip]http://members.shaw.ca/divineone/DDSaveEdit0[1].2.0b-MinDepend.zip 
