For this rewarding program, lasting just over an hour, Mr. Wosner began with Schubert’s Sonata in D (D. 850), sometimes called the “Gasteiner” because it was composed during three weeks in 1825 when Schubert was staying in Bad Gastein, an Austrian spa town. Then Mr. Wosner was joined by Hyunah Yu, a gifted young South Korean-born soprano, in six Mahler songs from “Des Knaben Wunderhorn.”