Where find a key to open small box on shelf in house farm.
Farm of Carl Jackson with his wife Dana (Broken Valley outside).

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And how to open wood door inside unerground cellar near this farm(if go from this farm to village Broken Valley, not to crossing the bridge).
P.S. Also behind this door can be seen walking goblin-shaman)

Thnks.

If I remember correctly there are two keys in his house. One from his cellar up on some beams and one behind some barrels. The good thing to do whenever you find a locked recipient is to look around, the key is always someplace near.

About the cellar near his farm, I'm not sure but I only found about it and opened it when I did the bandit quest (jailbreak). Maybe it's inaccessible for now?