One of the most amusing shows recently has been staged far off Broadway, down at the big building which houses the New York state Supreme Court, where Helen Kane's boop-a-dooping suit against a movie concern has been heard. Heard and seen. Frivolous films have been projected in the judge's chambers, and the presiding justice has listened gravely to an ansortment of boops. Mae Questel, Bonnie Poe and Margie Hines, rival doopers for the defense, sat around and looked very bored. Helen herself, thinner than she used to be sat in a corner, meditatively sucked a finger, and now and then beamed at her husband, Max Hoffman, Jr.