It can be sometimes be difficult to select NPCs or objects when they are surrounded by several player characters. However, holding the "X" key will temporarily hide player nameplates, making it much easier to select your desired target. This is known as a "target filter," and is especially useful when many player characters are on the screen at once.

Assigning Keys
The keys used for target filtering can be changed by using the Target Filters option, accessed from the System menu, followed by Keybind, and then the System tab.

Select either Key Setting 1 or 2 and press the key you wish to use. Changes will be saved when you press the Apply button.