Mnaseas is reckoned to have been a pupil of a scholar who was chief librarian at what library?
Mnaseas: Mnaseas of Patrae (Ancient Greek: Μνασέας ὁ Πατρεύς ) or of Patara, whether that in Lycia or perhaps the Patara in Cappadocia was a Greek historian of the late 3rd century BCE, who is reckoned to have been a pupil in Alexandria of Eratosthenes. Eratosthenes:  He was a man of learning, becoming the chief librarian at the Library of Alexandria.
Library of Alexandria