Where does Air Force One refuel?
According to the Washington Post, Air Force One never refueled in mid-air with the president on board.
If it needs to refuel, it usually does so at one of the U.S. military bases across the world.

The retrofitted Boeing 747 that usually serves as the presidential jet can indeed refuel in flight — but it has never done so with the president on board, military officials say.
It has enough range to fly from Washington to Iraq without needing more fuel. On longer trips to Asia, it typically stops at U.S. military bases in Alaska or Germany.
— Five myths about presidential travel