According to an article on Space.com,
The dummy is part of a full suite of sensors aboard the uncrewed mission, which will produce data that SpaceX and NASA will rely on for future, crewed missions. "We instrumented the crap out of this vehicle; it's got data, sensors everywhere," Kathy Lueders, manager for NASA's Commercial Crew Program, said during the news conference. "Actually having a re-entry, with Ripley in the seat, in the position, is critical."
The sensors inside the Ripley dummy will measure forces and acceleration experienced by a future human passenger, as well as the environment around them.
Yes, they named the mannequin "Ripley"