The Sleight of Hand badge is for "Unlocking 100 containers"
Containers are any storage device that has a lock on it (Appears as a colour coded padlock). To unlock it you simply need to have a lockpick in your inventory and complete the colour matching mini-game.
All trials have a similar number of locked containers so simply play the one you are most familiar with repeatedly to unlock this.
Also two handy things to note:
1. The in-game badge menu tracks your progress.
2. Leaving a trial after gaining progress still counts towards it.
Video guide for reference: