What is the pesicha of Omnon Ken on Kol Nidre night? When does it occur, and on what page of the Artscrol Siddur can it be found?
After the Amida on Kol Nidrei night, there are a few paragraphs of Selichot that are said.
The 3rd or 4th starts with the words Omnon Ken - and the Aaron HaKodesh is opened while saying it - hence "pesicha of Omnon Ken".
It's on page 175 of the Interlinear ArtScroll Yom Kippour Machzor, Ashkenaz edition.