Epic poem does the god Krishna teach the prince about duty

The answer here is that the epic poem in which the god Krishna teaches the prince about duty is the Bhagavad-Gita. In the Bhagavad-Gita Krishna talks about the importance of doing your own duty, and doing it despite what others think or whether your cause destruction in your wake. Krishna states it is better to do this, than to try to follow the path of another.