Complex sentence: He studied music theory from April to July 1890 with Hugo Riemann at the royal conservatory in Sondershausen and continued his studies, piano and theory, at the Wiesbaden Conservatory from September that year.
Split into simpler sentences: He studied music theory from April to July 1890 with Hugo Riemann at the royal conservatory in Sondershausen. He continued his studies, piano and theory, at the Wiesbaden Conservatory from September that year.