Step 1) Hunt down the thread with entire questline (yes, there is one, no, I am way too lazy to do it myself)
Step 2) Download one of the addons that tells if you completed a certain quest or not. Queststate is the one I use, but I think there are other ones.
Step 3) Check quests one by one to find out where in questline you lost it.
This is all presuming that basic methods, such as "available quests" and "NPC search" don't help.
If your questline is lost in Limo near Oasis, be aware that you need to complete both Return The Glory and Envoy of the Dragons line before they merge and you get the next quest. There are 3 or 4 opening up in Limo, then you are off to LOM
-- Rustyx --- 92R / 92S / 92M on Reni (Guild KnightShift). Yes, running the new FOTM R/M, cause I am not elf enough to be WD/S.
Oh, and people who have more than 3 classes are clinically insane.