I am a citizen of Pakistan, but I graduated from medical school in the United States. Do I have to receive ECFMG certification in order to apply for J-1 visa sponsorship of a clinical graduate medical education program?

No. Only international medical graduates (IMGs) must be ECFMG certified. An international medical graduate is defined by ECFMG as a physician who received his or her basic medical degree from a medical school located outside of the United States and Canada. It is the location of the medical school, rather than the citizenship of the physician, which determines whether the physician is an IMG. As the physician in this question graduated from a U.S. medical school, he or she does not need ECFMG certification.