Yes, it is the present progressive, or present continuous, in Italian. "When are you writing?" is a valid translation of "Quando scrivi?" The present continuous in Italian is more restricted -it is about what is happening in the moment (in progress). In fact, it would be a bit weird to ask "quando" with "stai scrivendo?" because the grammar implies the time: right now!
in italiano il presente progressivo praticamente non si usa. I play tennis= io gioco a tennis può essere un'affermazione come un'attività che sto svolgendo mentre i am payng tennis vuol dire che io sto giocando a tennis, cioè in questo momento compio l'azione di giocare mentre la frase io gioco a tennis vuol dire sia che sto giocando che il fatto che io sia capace di giocare a tennis. è molto complicato, come è complicato per noi usare in inglese il present continuous. Ciao
The present continuous is never used for the future, but the present can be used this way. It's common to use the simple present in Italian to describe the near future, similarly to how we use the present continuous in English. For example: "Domani vado in biblioteca" (Tomorrow I'm going to the library.), or "Vieni alla festa stasera?" (Are you coming to the party tonight?).
No, I don't believe the present progressive is ever used for the future in Italian - it is always about what is happening right now - significantly different from English. However, you can use past and even future forms of stare + gerund to indicate what was / will be in progress at that time. Eg stavo leggendo in quel momento = I was reading at that moment. Starò cantando = I will be singing
I also think it could mean "when will you write?" For instance depending on the inflection - my cousin and I write (letters) to each other (American to Italy and back) and this is a common question between us. It could mean "time" as in when do you write (like when do you do your writing - in the morning, afternoon, evening, etc.) or when will you write - when will you write (me a letter) again?
What sort of question is this? I answered: "When will you write?" and scored incorrect. The answer to when do you write is indistinguishable from the answer to the question I posed.
When will you write? Tomorrow, after I arrive home. When do you write? Tomorrow, after I arrive home.
When will you write? When I am asked to turn over the exam booklet. When do you write? When I am asked to turn over the exam booklet.
When will you write? I have wrtier's block and won't overcome it until I've had a long bath. When do you write? I have wrtier's block and won't overcome it until I've had a long bath.
I could go on...
They're two separate words (in Spanish as well): quando (when) and quanto (how much/how many). If you're having trouble telling them apart, think of "quanTity" to remember that the word for "how many" has a T. Spanish is just the same, but the words are spelled with a C (cuándo, cuánto).