Learn Italian: Non superare la dose massima. - Do not exceed the maximum dose.

This is the Jussive Infinitive (Infinito Iussivo). It is used for impersonal or general instructions where you aren't addressing a specific person. You will see it constantly on medicine labels, recipes, instruction manuals, and public signs.

Since the negative informal imperative also uses non + infinitive, how do we know this is the Jussive Infinitive?

The context gives it away. Medicine warnings are aimed at the general public, not directly at you as an individual. If this label had an affirmative instruction, it would still use the infinitive (like assumere con acqua), whereas the informal tu imperative would change to a conjugated verb (assumi).

If we wanted to replace la dose with a pronoun to say 'Do not exceed it', how would we attach it?

You would drop the final -e of the infinitive and attach the pronoun directly to the end. To say 'Do not exceed it' (referring to the feminine noun la dose), the phrase becomes non superarla.

Why is massima placed after dose when adjectives like massimo often go before the noun?

While you might see massima before a noun in figurative phrases (like la massima attenzione), here it acts as a strict classifying adjective. It puts the dose into a technical medical category, much like velocità massima (top speed), so it must follow the noun.