If you're after completing this achievement ASAP, open the spoiler. If you are after enjoying the story without spoiler, just continue playing as you would and this will eventually unlock.
*** Spoiler - click to reveal ***
Continue heading down the minecart track. Jump off when prompted. Jack and yourself will end up on a ledge. Some guys in animal's clothes will come to the edge and propose a deal. Your swords for their help to get you off the ledge.
If you refuse the deal, Jack will fall. (but you keep your sword)
If you accept it, you lose your swords but both yourself and Jack are saved.
You will encounter another stranger, which will lead you to a community of people living around Fred's house. You have to win a contest to enter the keep. Once you get control over your character, you can immediately head over to Binta, as the answers to her questions are already known. Start by placing some blocks to look like Fred. The round will become a draw.
After that, there are 4 questions which Binta will ask, first one is for Kent.
What's Fred's favourite food? --> Bread
Your question will be: What's fred's favourite colour blue?
Answer: Lapis Blue
Kent will get the question: What is Fred's favourite tool? --> Diamond Hoe
You will get the question: What is the name of Fred's favourite companion?
Answer: Waffles
The last question is decisive and both you and Kent can answer:
What is Fred's favourite tree type?
Answer: Birch
Kent will complain about it not being known, but you get to spent the night in the Keep.
Once in the Keep, head over to the closet in the back of the room and press the button on the inside. Once in the secret room, read the book on the right hand side of the room and have a look at the map in the back to find out more about what the situation was down here.
Head out to look for the cabin. You'll have a short conversation with Binta, after which she gives you here compass, which points towards home.