Answer
The answer is Antioch. Nikephoros II's military campaigns were primarily focused on the eastern and southern borders of the Byzantine Empire, particularly against the Arabs and Bulgarians. While he achieved significant victories and reconquered several territories, Antioch remained under the control of the Arabs throughout his reign and was not reconquered by the Byzantines until 969 under the reign of Nikephoros' successor, John I Tzimiskes.