While both places you'll need to visit are mentioned in the quest's description, the Locate function isn't reliable. Here's some advice to Lost Ark Boosting finish that Stone of Power quest.

To complete this Roster quest, you'll have to collect 15 pieces of Shadowfallen Giant Locarok, stone fragments of Pebbling and the 4th Claw of Thanatos.To take the pieces along with the stone fragments, you'll have to head to the dungeon that is located on Tortoyk Island, called Tortoyk's Heart.

Since you won't have to finish the entire quest in order to acquire all of the necessary items that you'll need from this quest it's possible to start a queue and leave whenever you want in order to speed up your journey.

You'll have to head to another dungeon for to find the fourth Claw of Thanatos. Travel to the continent Yudia located in the Saland Hill area, and enter the Morai Ruins dungeon. The dungeon will require you to complete this time. You'll get the item given to the final boss.

When all the materials have been gathered, you'll be able to Buy Lost Ark Boosting collect the rewards and end the quest directly from in the Quests menu.