The goblins are central to the game's plot in Hogwarts Legacy. This quest is especially important because it will allow you to learn how to petrify your foes at a later time. However, at some point early in the quest, you'll be asked to investigate the "Goblin Presence."
Here's all you need to know about how to investigate Percival Rackham's Hogwarts Legacy goblin presence.
How to Finish Percival Rackham's Trial in Hogwarts Legacy while investigating the goblin presence
To progress through the quest, go to the ruin indicated on your map. Look around you and you'll see a large tent near pillars in ruins. Head inside to find the item you need.
You're looking for the letter sitting on a table, specifically. By reading it, you'll progress to the next stage of the quest.
Next, go out of the tent and repel the goblin slugs that will spawn. Once the enemies are cleared, you'll be able to follow the NPC to the next stage of the game. The enemies shouldn't cause you too much trouble at this stage.