@Alone-zee Ideally one can eventually get beyond the /nj/ approximation to /ɲ/ itself. Since that nasal is palatal it's inevitable that you articulate (or perceive, in any case) the palatal off-glide /j/ when transitioning to another vowel. If the question comes down to whether <gn> may ever be approximated /n/, or always /nj/, the answer is always /nj/ since that's closer to its true pronunciation /ɲ/.

I don't know if there are any critical pairs in French (probably not since there are hardly any -nio-), but I know there are many in Italian. I remember the first time someone tried to show me the difference. I really couldn't tell.

Ah wait, maybe there are with conjugated verb forms.