This article describes how the Zero-Dose Learning Hub convened national stakeholders in Nigeria to develop a coordinated learning agenda to identify and reach zero-dose and under-immunized children. Using a three-round modified Delphi process, participants prioritized 10 key learning questions across equity, health systems, and innovation. The highest priorities focus on identifying and monitoring ZD children—understanding who and where they are, why they are missed, and the system-level factors affecting their measurement. The resulting agenda provides a nationally owned roadmap to guide evidence generation, inform program design, and support more targeted immunization efforts.