Complex sentence: The Yeshiva was named "Shaar HaTorah", after the yeshiva in Grodno in Europe, at which Rabbi Epstein's great-grandfather, Rabbi Shimon Shkop had been the rosh yeshiva.
Split into simpler sentences: The Yeshiva was named "Shaar HaTorah", after the yeshiva in Grodno in Europe. Where Rabbi Epstein's great-grandfather, Rabbi Shimon Shkop had been the rosh yeshiva.