THE SOLOIST by Mark Salzman (Vintage: $11; 284 pp.). Renne Sundheimer, the narrator of Salzman's intriguing novel, is a musical has-been, a prodigy whose career as a cellist has foundered in neurosis. Withdrawn to the point of near-catatonia, Sundheimer half-heartedly teaches at a university until jury duty and the appearance of a dazzlingly talented Korean boy transform his drab existence. Salzman reflects on the nature of the master-student bond and the desire to pass understanding and even enlightenment on to the succeeding generation in this gracefully written novel. Like a Zen koan, "The Soloist" is simultaneously entertaining and thought-provoking.