"Cognoscenti" is the plural of "cognoscente". It means "the people who know (a particular subject) thoroughly", or "the people who are expert in (a particular subject)". It's sometimes used ironically.
1. The ordinary blues enthusiast will not be particularly interested in the three newly discovered versions of Robert Johnson's "Crossroads Blues" which are to be found on this CD. But the cognoscenti will be fascinated by the variations in the bass line and the differing lyrics in versions #2 and #3.
2. Most visitors to the gallery will pass by Morandi's paintings of jugs and bottles without a second glance. To the cognoscenti, however, their muted greys, browns, and blues are endlessly appealing.
I should have added that "cognoscenti" tends to appear in discussions of the arts; it would be unusual to find it in the context of sub-atomic particles, or butterfly genitalia, or the Poisson distribution.
Indeed. Italian and I have been muckers (old friends) since long before the time of Dante Alighieri, and from time to time I lose track of the state of play, as far as etymology is concerned. There was a G there if you go back far enough - though I'm not sure how far.