Complex sentence: In November 1894, S. I. Taneev (at M. I. Tchaikovsky's request) began to study the unfinished sketches of these two movements: I have copied out from Petr Il’ich's notebooks sketches for two movements of a future piano piece.
Split into simpler sentences: In November 1894, Taneev began to study the unfinished sketches of these two movements. He wrote Modest, I have copied out from Petr Il’ich's notebooks sketches for two movements of a future piano piece.