Which cabinet department would most likely be responsible for enforcing each order?

Overseeing criminal investigation agencies such as the FBI

Overseeing criminal investigation would be a task for the Department of Justice. This department is in charge of the enforcement of the Law.

Receiving ambassadors from other countries is the responsibility of Department of State. This department advises the President and is responsible for representing the country in international affairs.

Gathering Army and Reserve Forces to defend the country is the responsibility of the Department of Defense. This department is responsible for the armed forces and all matters concerning national security.