where would you find hemoglobin that is about 65% saturated with o2 in a healthy resting person?

You would find hemoglobin that is about 65% saturated with O₂ in the blood of systemic tissues/standard systemic venous blood , such as in the venous blood returning from actively metabolizing tissues to the right side of the heart (for example, in the pulmonary artery or a systemic vein of a healthy resting person). On the classic oxyhemoglobin dissociation curve, a saturation around 65–75% corresponds to a partial pressure of oxygen around 40 mmHg, which is the typical PO2P_{O2}PO2​ found in mixed venous blood draining resting tissues.