On Sunday, at Alek Shrader's Schwabacher Debut Recital in Temple Emanu-El, presented by the San Francisco Opera, I was wondering about the tenor's response if Barbara Walters should ask him what kind of tree he would be. Not knowing the answer, I came up with a question to which the answer is obvious. What kind of drinking glass would Shrader be? Tall, clear, gracefully simple, and full.