There seem to be three terms used by experts in the field In that context, which is more correct or more frequently used However, the other two seem to be more commonly used in that context.
Non, non et non ! | l'école des loisirs
Except non is not an english word, it is a prefix of latin origin
Which is why american style manuals will always ask you to merge it with the subsequent word, without a hyphen
Leaving non stranded doesn't work either as it is a bound morpheme, a prefix not a word (in english) I'd use the two hyphens.
