Successfully detecting a character's thoughts is a fairly simple action that is available quite often in the game. To do so simply requires the ability to cast detect thoughts, whether through the use of a scroll or actual spell. Luckily, Shadowheart comes equipped with a detect thoughts scroll should you either recruit or kill her. Once you can cast detect thoughts, it's simply a matter of speaking to someone with a [Detect Thoughts] dialogue option, which is fairly common. Doing so will automatically cast detect thoughts on your character and make you pass a check to successfully detect the person's thoughts. Passing one such check will make this trophy pop.

If you're having difficulty finding someone to detect the thoughts of, there are plenty of opportunities to make use of in the Goblin Camp of act one. Simply start a save as Shadowheart (or recruit her) and make use of her scroll to detect the thoughts of one of the goblins. There will be opportunities with many of the guards posted around the Goblin Camp that try to stop you as well as with different goblins on the side you can interact with (such as the one making a gnome "fly").