This quest is available once you complete main quest: Get Junior, and secondary quest: Now or Never.

Start the quest off by talking with Dijkstra. Roche turns up and says he's in on the plan also.

Geralt must now head to find Dijkstra's agent, who has failed to check-in.

Leave the building and use a fast travel point and head to the Redanian checkpoint, and talking to one of Dijkstra's Redanian agents, Gregor.

Gregor tells Geralt where he could find the Shoemaker's wagon. Head to the map marker til you discover the wagon. You'll need to use witcher senses from there to follow the trail of shoes.

You will eventually come across a Troll, surrounded by lots of "shoeses". Talking to him will lead him to tell you that two of his troll friends have taken the shoemaker away with them to a nearby cave.

Depending on your dialogue options with the two trolls, you can convince them to let the shoemaker go without a fight. After dealing with these trolls, escort Thaler back to his shoe cart.

You may also be able to play Thaler at Gwent at this point.