If you have Radiant Echo in your Bags, you will have to look the Map for "Worldsoul Memory" events.
Go there, click on a bright yellow-blue sphere and you'll be teleported in a zone where you will need to kill as many mobs as possible.
Some rare elites will also spawn, but they're manageable.EDIT:
I had a quest in "Isle of Dorn", but i completed mine in Undermine. You need to go to a "World Sould Memory" event.
Quest
A Radiant Echo
A World of Warcraft quest in Dornogal. Facts and objectives from the current retail game data.
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For those who don't get how to hand it in or where - you just have to click the quest itself to hand it over.
I have the Radiant Echo in my inventory and whenever I get to a worldsoul memory spot, the glowing orb that is supposed to be there is no longer visible and clicking the Radiant Echo does nothing. I've tried this in several spots.
Quest facts
The client quest POI data records no map location for this quest, so no map is shown.
Check whether you have already completed this quest
in-game: /run print(C_QuestLog.IsQuestFlaggedCompleted(84542))
Description
<Within your hand, you hold a small Azerite sphere. Its light is steady and bright, but the sound it emits is plaintive and longing. It tugs at you, ever so slightly.>
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