Picked a pocket and a lock using the focus ability
Focus allows you to easily spot collectibles, objects you can interact with and also slows down time. To use you focus ability you press the button. Before you can obtain this achievement you must first use two focus points to level up your Dexterity focus ability. Focus points become available after you visit the Queen of Beggars just prior to beginning Chapter 2, after you visit she will automatically award you with one focus point and the ability to purchase more from her with a donation of gold. You can go directly back to her and purchase one more point allowing you to fully upgrade dexterity. Once you have done that you just need to pick a pocket and a lock whilst in focus mode and the achievement will unlock.
You don’t have to do both during a single activation of your focus ability.
To do this you must first upgrade the Focus ability "Dexterity" to its maximum level. You can buy focus upgrades from the Beggar's Queen in the most northern part of The City. After you've upgraded Dexterity, head to the glowing gate around the corner to start Chapter 2 (can be replayed at the same location if you've already beaten it). In the beginning of chapter 2 is a guard with two pockets and a locked door. Activate focus vision and pick the guard's pocket, as well as the lock of the closed door.
You can then pause the game and click "Return to the City" to get back to the Beggar's Queen.