Defeat Berserker Daradon is a quest available after Banshee Wetlands have been passed for the first time. It is part of the main quest line and becomes unavailable after it has been completed.
To complete the quest, 2 Berserker Daradon need to be killed in Banshee Wetlands. At least two dungeon runs are needed to achieve this, because only the single Berserker Daradon roaming around the dungeon counts, fighting off the Daradon waves in the Daradon Lair inside the dungeon does not count towards the quest goal.
Click on [Campaign] -> Select the [Banshee Wetlands] -> Kill 2 [Berserker Daradons]. The Berserker Daradons are some of the greatest beasts lurking in the darkness. Kill all of them to proceed.