Who was the teacher of R' Judah ben Meir HaKohen, and from which chain of tradition does he derive? I ask because I cannot find much information about him online, other than many references to his being the primary teacher of Rabbeinu Gershom. As Rabbeinu Gershom's role in shaping Ashkenazic Jewry cannot be understated, it would seem to be valuable to be able to trace his teachers and Mesorah.
Other than his father, the book Toldoth Yisrael cites the responsa of Solomon Luria (Shu"T RaShaL #29) as claiming that he was a student of Rav Hai Gaon. In the footnotes he discusses the plausibility of such a claim.