A new PBS documentary, “Defying the Nazis: The Sharps’ War,” tells the story of anti-Nazi heroes Martha and Waitstill Sharp. On Tuesday, the film will be screened at 4 pm in the Sperry Room, Andover Hall. A post-screening panel, at 5:45 pm, will include the Sharps’ grandson, Artemis Joukowsky, who collaborated with documentarian Ken Burns on the film. The Gazette spoke with Joukowsky about the project.