Hello,

Under EYSEK for "matter, issue" in the "Comprehensive Yiddish-English Dictionary", Beinfeld and Bochner, 2014, they list "have experience, be on top of things" for "farshteyn an EYSEK". They also list "farshteyst an EYSEK?" as "get it? understand?".

I hope that might be helpful. I am familiar with the word EYSEK, but not this particular expression.

Al dos guts,
Yosele

I believe the word 'Esik' also means vinegar. I am not sure of the meaning of the phrase or how it is used, but perhaps we can figure it out.