An initial word of caution. DNA analysis is a combination of science and statistics. If either is incorrect, the results will also be incorrect. Since statistics are involved, we are dealing with probabilities, not certainties.
An 8% Ashkenazi Jewish ancestry is about what one would expect if one of your great-great-grandparents had 100% Ashkenazi Jewish ancestry, and none of your other ancestors had any.
Y-DNA analysis will not help you if you are certain that Jewish DNA does not occur in your male line because Y-DNA looks only at the Y chromosome, which is passed nearly intact from father to son. Any female in that chain renders the test useless.
There is probably no alternative to following the records back. One might pay particular attention to female ancestors who lived in areas where significant number of Ashkenazi Jews lived.
Professor of Law, University of San Diego
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Author: Mastering Art Law (Carolina Academic Press, 2d ed. 2020)