bailiwick

The district within which a bailie or bailiff has jurisdiction.

The Bailiwick of Jersey.

A person's concern or sphere of operations, their area of skill or authority.

I established the fairly well-understood pattern that affairs of state were not in my bailiwick.

Jack is full of these insights, thoughtful turns of phrase from a character whose perpetual struggle between wastrel and righteous is all too familiar a bailiwick for the universal insecurities of the human condition.