This note, is written there in the English-game-version "Atiic" or "Storage Cellar"?
(I'm playing the German version and don't have the English version at hand right now)
I understand in this context only so much that Jespar's sister rented this cellar to present the corpse there. The farmer probably didn't want to rent it to her so cheaply.
You are already standing in the room in question, so there is nothing more to find.
PS:
if there is "Atiic" instead of "Storage Cellar" in the game, you could possibly write a bug-ticket, topic: Suggestion