You should shoot the voice coach who told you how to pronounce naivety - I'm sorry, I mean naiver-TAY.
I jest, it wasn't half bad, I guess.
Naiveté... naivety isn't a word.
Pronounced usually just as he'd done it, though Naiv-tay also works. I remember that caused an embarassing moment for me the first time I pronounced it asking what it meant, sounding as "corvette".
Of course, that's why the Oxford dictionary has naivety listed as a word with a definition then.
noun (plural naiveties)
lack of experience, wisdom, or judgement:
his appalling naivety in going to the press
innocence or unsophistication:
the charm and naivety of the early to mid fifties
[count noun] a naive act.