Direct answer
Objectives follow journal display order. Some depend on your choices; follow the active objective in the game.
Result
Yennefer asked - or rather, if I am to be completely honest with you, dear reader, ordered - Geralt to help Eskel hunt a forktail. The sorceress needed ingredients from this dangerous beast's body and clearly thought two witchers would get the job done sooner than one. Geralt thus set out to track the monster - but first, he had to find Eskel.
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