To unlock Jorvik City, you need to be level 9, Star Rider, and have finished the quests where you help James get his deliveries from the Jorvik City Mall. Once you have accomplished this, you will go on a quest called “The Flowery Janitor,” which will start your adventure to Jorvik City.
It’s easy to miss that you need to give Jack B. his coffee to be able to continue with James’ quests in the mall. You’ll find him standing in the café, and if you have accidentally thrown away the cup of coffee you got for him, you can easily get a new one by sitting down at one of the tables, opening the menu, and get a cup of coffee in exchange for Jorvik Shillings. Once it is in your backpack you can give it to Jack.