Direct answer
Objectives follow journal display order. Some depend on your choices; follow the active objective in the game.
Result
A short distance from Castel Ravello, Geralt happened on a notice posted by Jacob, a lumberjack. The logger was in search of someone who had no fear of spells and could thus face a witch. This was the very description of the witcher, no two ways about it, so it was no surprise that our hero took an interest in the notice and decided to visit Jacob.
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