Complex sentence: Rabbi Yosef Shlomo Kahaneman (1886--1969), was its rosh yeshiva (head) and president, who became known as the "Ponovezher Rov" was the head of the yeshiva and was also the leading rabbi of Panevėžys.
Split into simpler sentences: Rabbi Yosef Shlomo Kahaneman (1886--1969), was its rosh yeshiva (head) and president. Known as the "Ponovezher Rov", he was also the leading rabbi of Panevėžys.