President Joe Biden Friday said the U.S. does not know what has happened to at least two Americans who have gone missing while fighting in Ukraine. The commander-in-chief repeated warnings against Americans volunteering to fight on the side of the Ukraine government, regardless of how strongly they support Kyiv’s cause. “We don’t know where they are,” Biden told reporters as he headed home to Delaware for the weekend. “I want to reiterate, Americans should not be going to Ukraine now.” “I’ll say it again: ‘Americans should not be going to Ukraine,’” he added. Two U.S. veterans who were fightin…