Here's a brief explanation how doppelgangers work:
Essentially the goal of a doppelganger is to replace someone, a government official, a major general, or a ruler, with an exact copy that can be used as a puppet controlled by the one who cast the spell. Doppelgangers are created by taking the essence of someone (usually some strands of hair) and combining it with clay to create a new body that appears just like the original.
The new body has no mind of its own, no soul, merely an empty shell resembling life.
Doppelgangers make excellent assassins as the person who controls them cannot feel the pain or damage inflicted onto the double. The puppeteer can control the doppelganger's actions from any distance, and can dictate their movements and actions remotely. Should the puppeteer let go of control temporarily, the doppelganger will merely stare ahead, as if lost in thought. It can still stand, breathe, and even be led around by others, but it cannot move or speak on its own.
When a puppeteer controls a doppelanger, they usually get a first-person point of view through the eyes of the double. However, Vellian included an additional spell for her to watch the doppelganger in a third-person POV as you're seeing above.