Narrow negation, where scope of negation falls on an argument or adjunct rather than on the entire proposition can be marked by the syntactic position of the negator, as in John 12:9:
καὶ ἦλθον οὐ διὰ τὸν Ἰησοῦν μόνον, ἀλλʼ ἵνα καὶ τὸν Λάζαρον ἴδωσιν ὃν ἤγειρεν ἐκ νεκρῶν.
Another example is John 12:30, where the negator with its argument scope are fronted before the predicate together:
Οὐ διʼ ἐμὲ ἡ φωνὴ αὕτη γέγονεν ἀλλὰ διʼ ὑμᾶς.
Examples of negation like this one
represented marked usage. The syntactic position explicitly denotes the negation scope.
Still, it is essential to take note that the markedness of narrow negation scope is asymmetrical. The syntactic position of the negator only means something for interpreting negation scope when it is moved out of its normal preverbal position. It have scope over the proposition. We know this position can be used for not only clause scope negation, but also argument scope negation because of examples like John 12:44:
Ὁ πιστεύων εἰς ἐμὲ οὐ πιστεύει εἰς ἐμὲ ἀλλὰ εἰς τὸν πέμψαντά με.
In sum: the syntactic position of the negator matters for interpretation when the negator is moved out of its normal immediately pre-verbal position. Otherwise, if it does not and remains in the default spot, then negation scope must be interpreted via contextual clues.
On this view, the correct interpretation of a clause such as this one from John 12:35, should take the scope of the first negator μὴ as narrow over σκοτία rather than over the verb. In this case, the negation scope could be rendered into English as, “so that no darkness will overtake you.”
περιπατεῖτε ὡς τὸ φῶς ἔχετε, ἵνα μὴ σκοτία ὑμᾶς καταλάβῃ, καὶ ὁ περιπατῶν ἐν τῇ σκοτίᾳ οὐκ οἶδεν ποῦ ὑπάγει.
The second negator οὐκ is unmarked for scope, but the context best suggests scope over the whole proposition/clause.