Given enough distance from a tragedy, some comedians will try to add levity to the situation. This hour, we’ll talk about if it will ever not be “too soon” to crack a joke about the Holocaust with Ferne Pearlstein. She explores one of comedy’s most taboo topics with Mel Brooks, Louis C.K., Chris Rock and other comedians in her documentary “The Last Laugh,” which screens Thursday as part of Videofest.