Complex sentence: In the Drawing School of St. Petersburg he continues to improve his skills and create paintings, one of the best paintings of the period- "Portrait of the artist's younger sister, Yekaterina Sychkova" (1893).
Split into simpler sentences: In the Drawing School of St. Petersburg he continued to improve his skills and create paintings. One of the best paintings of the period is "Portrait of the Artist's Younger Sister, Yekaterina Sychkova" (1893).