To activate the grave of Someone Forgotten on the Coiled Isle in World of Warcraft (Patch 12.1, The Midnight expansion), you need to complete a short puzzle involving three NPCs.
The Forgotten Soldier grave puzzle
On the Coiled Isle, there is a grave tied to a “Forgotten Soldier.” Interacting with it starts a clue-based sequence. The first clue you receive is “Jin’tha.”
To solve it, speak to three specific NPCs in the correct order. One of them is Zuzan, who sits just north of the Ring of Glory, by the walls around the vendor area on the Coiled Isle.
Once you’ve spoken to all three NPCs in the proper sequence, return to the grave. The Forgotten Soldier will no longer be there, and the grave becomes lootable, rewarding you with a treasure.
This is a self-contained world puzzle on the Coiled Isle; it doesn’t require a quest log entry or a long chain, just finding and talking to the right NPCs after the initial grave interaction.