I think that the reader has the option of deciding whether it is first, second, or third person in many subjunctives. "Do you want her to make coffee" or "Do you want me to make coffee" are said the same way. The only one it can't be is second person here, since the sentence starts with Vuoi and the subjects must be different.
Question: Is the Italian expression "Per quanto ..." always directly followed by the Subjunctive? Asking because in English for me "As far as I know ..." is just another way of saying "I believe ..." or "I think ...". So not what I think or believe or (as far as) I know is the presumption but him being American. So: "As far as I know he is American" = Per quanto ne so, lui sia Americano. Wrong?
It is a correct sentence. "per quanto" may mean "although" and "as far as" in Italian. When it has the second meaning, the verb which follows can be conjugated in the indicative or in the subjunctive mood. The verb in the main clause always remains in the indicative mood.
The subjunctive indicates doubt or uncertainty. Therefore if you are uncertain....ie. you only think so, but you are not sure in your own mind, the subjunctive seems right. To my mind that uncertainty must naturally extend to the second part of the sentence. However, although I've been in Italy for a year or so and done several language courses, I'd still want to check that with an Italian person.....although as one teacher said to me 'don't worry too much, many Italians don't even know when to use the subjunctive'.
Sometimes it helps to internalise the per quanto in this sense. If you were trying to translate into Italian, many of the "good English" translations would be nonsense in Italian . Whatever method that gets you to good Italian. The other direction matters less when reading Italian as you can get a good gist and use your knowledge of English