There are two kinds of Khazar:

Harkavy was responsible for spreading the idea that the Kuban-Khazars converted to Judaism but there is no evidence that the Kuban Khazars adopted Judaism rather than a religion referred to in Christian sources as the Heresy of Zembra the Khazar in the 860s. It is possible that Zembra followed the religion of the Taurian Godfearers. Before Harkavy there was Benjamin Aga who argued that his religion was descended from Kuban Khazars. But the only evidence of anything remotely Judaic from Kuban-Khazaria is an Arabic "Musa" coin which might rather indicate an heretical Islamic sect. Some have tried to argue that a six-flamed sun-disk symbol discovered resembles a Magen David.