Which of the following provides plans, policies, and guidance on Service member issues?

The Department of Defense (DoD) is the correct choice because it is the federal department responsible for coordinating and overseeing all agencies and functions of the government related directly to national security and the military. Within the DoD, various policies and guidelines are created to address the welfare and needs of service members, encompassing a wide range of areas including personnel management, recruiting, training, and quality of life initiatives. By setting overarching plans, policies, and guidance, the DoD ensures that all service members receive consistent support and resources across different branches of the military.

In contrast, while the Joint Staff and Service Headquarters play essential roles in advising and managing military operations and functions, they do not solely focus on the broader policies concerning all service members. The Personnel Support Office, although vital at the local or unit level for providing administrative support and services directly to personnel, does not operate at the strategic level necessary for establishing comprehensive plans and policies affecting all service members across various branches.