There is a useful article The Limits of ancestry DNA Tests,explained.Brian Resnick May 23,2019 -site -health/2019. The article provides an overview of the DNA tests and what they can and can't do. It is written in user friendly language. There is a very brief reference to Ashkenazi Jews and the effects of the diaspora and close marriage on their DNA.
There are other articles on the subject elsewhere and on the BG DNA Forum.