California State Atty. Gen. Kamala D. Harris has subpoenaed CitiGroup Inc. and its banking subsidiary, CitiBank, ordering the two entities to answer questions regarding the selling and marketing of mortgage-backed securities in the Golden State, a person familiar with the investigation said. The person, who was not authorized to speak publicly about the matter and spoke on condition of anonymity, would not further characterize the nature of the investigation. Spokespeople for the attorney general’s office and Citi declined to comment.