This is story related and therefore unmissable. If you want to know roughly when you get it be aware the it does say SPOILER.
*** Spoiler - click to reveal ***After returning to Skallitz to bury your parents and being brutally bludgeoned by Runt,
you wake up in Theresa's uncles house, just North of Rattay. Your objective should take you to the castle at Rattay, where a scene plays out in the dining hall.
After this cutscene the achievement should unlock
Hope this helps,
Let's keep cheevin' together!