This quest does not show up in your journal. In actuality it is more of an event. It is being listed as a quest to make it easier to understand how to do it.
At the top of The Last Stand, there is a book titled "Feeding the Guurok". The black book is on the table.
Read the book it says: "When the Guurok near must be fed. Guurok eats skulls, but not gobbie skulls. It's people! Good thing graveyard near. Bring more gobbies in case angered. Six peoples it needs from on rock." The only option is to stop reading the book.
On the Colony when some of the skeletons are killed, they drop Pirate Skulls these skulls drop onto the floor and must be harvested. Collect 6 pirate skulls and take them to the rock near The Gurrock at -31.66, 1.68, -190.35. Examine the skulls 1 at a time and The Guurok will devour them and grow in size after each one. After the 6th skull, he aggros as a Level 6 ^^^.
The reward for this quest is The Guurok's loot table, which is quite good.