Geralt did the unexpected - he actually listened. Quietly, spare a few 'hmm's when it felt appropriate to what Jaskier was saying or he needed to put something small into the conversation opinion-wise.
"I've not visited Oxenfort yet. I'd like to. Their alchemy is spoken of widely." And he figured it would help if he could learn a thing or two from them. Geralt was sure he didn't know it all.