At first it looks tuscanian to me
I'd relate it to "Gne-gne" which refers to an immature lady (a baby crying)
In the web I found "Gnugna" adjective, indicating a nice but stupid girl, which then it's probably the same as above
"Gnugna" name then also indicates a female's sex.
Compare it to "Gnocca" = (emilian adriatic dialect): very nice girl / female's sex
and also "Gnucco" (north Italy) = hard thing / stupid, obtuse person
---------------- We can therefore define that word with the generic meaning as "inane", empty.