In order to learn the last bits of information Luadius has for you on how best to use your breath weapons, you are being sent underground into the labyrinth known as Dralnok's Doom. There you will fight against the Murk Crabs and prove yourself worthy of knowing all that Luadius does about the use of breath weapons.
Beneath Delgarath lies a set of caves known as Dralnok's Doom. You must prove yourself worthy to enter the labyrinth by having completed other quests, but once you have done so you are free to enter at any time. Travel there and seek out the pools that contain the Murk Crabs. Kill 20 crabs then return to Luadius with what you discovered.
Return to Luadius in Dralk to discuss what you have learned.