It's in Kamenets (Каменецкий уезд) Описи 17, 18, 19, 20, 21)
Just to give an example, I used this pathway (Notary records) twice. Once I asked for a rare surname and got super useful results. Another time I asked for a common name Frankel, and there was nothing useful in the county (uezd) I needed, but there were lots of records in other nearby locations. Specifically in Kaments uezd, there were two in Opis 17 (17-41, 255), three in Opis 19 (19-5101, 5462, 6503) and one in 21-10202. If I wanted to get the full headings of all these Kamenets Uezd notary records for the Frankels, then I'd out of further $30.