It got it using a Facebook personality quiz called «thisisyourdigitallife,» created for Cambridge Analytica by Cambridge University psychographics professor Aleksandr Kogan in 2014. (fortune.com)
The data was controlled by David Stillwell and Michal Kosinski at the University of Cambridge's The Psychometrics Center, but Alexandr Kogan, of Cambridge Analytica scandal fame, was also part of the project. (nypost.com)
NOTE: This question deals with a technicality related to how Congress hearings work, not about the actual content of Cambridge Analytica data scandal. (politics.stackexchange.com)