Jan Karski has a vitally important story to tell for anyone willing to listen. A member of the Polish underground resistance during World War II, Karski traveled around Poland observing Nazi atrocities, including inside the Warsaw Ghetto and the Belzec death camp. He then traveled to report on what he witnessed directly to people such as the British foreign secretary and U.S. President Franklin D. Roosevelt. They heard what he said but seemed not to heed it. Now actor David Strathairn, an Academy Award nominee for “Good Night and Good Luck,” tells Karski’s story at Berkeley Repertory Theatre in the...