The genetic, linguistic, and historical evidence conclusively refutes the "Khazar" hypothesis. Genetically, Sephardic, Mizahi, and Ashkenazi Jews are nearly indistinguishable. Linguistically, Yiddish comes from German and has no trace of Turkish. Historically, there is a continuous Jewish presence in Europe, extending from Ashkenaz (Franco-Germany) eastward.
The only people who repeat nonsense about the Khazars these days are Jew-hating Arabs, Jew-hating Black Hebrews, and so-called "Christian Identity" cultists.
And Arthur Koestler, the Hungarian Jew who wrote the book "The Thirteenth Tribe" and Shlomo Sand, professor of history at Tel Aviv University, who wrote the book "The Invention of the Jewish People".