Explanation:

• The Vinayapitaka is part of the Pali Canon in Theravada Buddhism.
• It primarily deals with monastic rules and regulations.
• Contains teachings of Buddha on monastic discipline and guidelines for monks and nuns.
• Option 1, Principles of religion is incorrect as it focuses specifically on monastic discipline.
• Option 2, Teachings of Buddha on discipline is correct, as the Vinayapitaka outlines rules for monastic practice.
• Option 3, Philosophical study of the ancient period is incorrect as it is more regulatory and practical in nature.
• Option 4, Duties of the king is incorrect as it does not pertain to governance or kingship.
• Option 2, Teachings of Buddha on discipline is correct.