In the final episode of "The Office", Jim decides to finally pursue a career in what field?

In the final episode of "The Office," Jim decides to finally pursue a career in sports marketing.

Jim’s opportunity comes through Athlead, a sports-marketing startup founded by his friends in Philadelphia. He initially invests in the company secretly, then begins splitting his time between Scranton and Philadelphia. The demanding schedule strains his marriage to Pam, but the business represents the ambitious career he had set aside while working at Dunder Mifflin.

By the series finale, the company has been renamed Athleap, and Jim is ready to return. Pam supports the decision and secretly sells the family’s Scranton house so the Halperts can move closer to Jim’s work. This gives Jim a chance to pursue his professional ambitions while keeping the family together.

A common mix-up is answering "sales" because Jim spent most of the series as a salesman at Dunder Mifflin. Sports marketing is the more specific field and the canonical answer.