Kids are prone to asking questions, like “where did I come from?” These become harder to answer when you’ve cloned your son, but no one’s really sure how many of them were made. In Caryl Churchill’s new play, A Number, there are no white coats or labs, just Sam Shepard playing the father, and a single actor playing three of his genetically identical offspring — each supposedly an improvement over the other. WNYC’s Judith Kampfner went to see the play with a psychologist and a medical ethicist.