I’ve been told it is three syllables.
Na with a long a, a (uh) man
Na a man
I used to be a lector and read it with two syllables. I got that from a list of Biblical pronunciations.
Our priest also read it with two syllables.
I SERIOUSLY doubt whether Naaman cares any more.
No one called her on it so I assume that it doesn't really matter.
My name is mispronounced often. Even if I TELL the person the correct pronunciation, I always hear the wrong one from them.
Old joke: Call me anything you like, just not late for dinner. :o)