Yes, it is a partitive article, but it isn't mandatory like in French; it's just that it's extremely hard to define where one should be used. "Vuoi zucchero?" feels incomplete, but it could be said in a colloquial context, while "vuoi zucchero o miele?" is perfectly normal in any context.
You can find two lessons on this issue on bussu.com :)
first: Il primo appuntamento
second: Trucchi per rimorchiare
Literally dello=di+lo, so "Vuoi dello zucchero?" is literally "Do you want of the sugar?" or a better translation "Do you want some sugar?".
Your sentence "Do you want some of the sugar" would be something like "Vuoi dello dello zucchero?" and this is not what you were asked to translate.
I think Duolingo needs to do a better job distinguishing between 2nd person singular and plural... It would help for them to say "you all" rather than "you", because it can sometimes get confusing and the lines get blurred. I know it accepts answers that say "you all", but it needs to urge it more in the beginning lessons so student can tell the difference.
The ‘do’ can be omitted in the English translation and a question mark placed at the end of the sentence, can it not? There is no Italian word for ‘do’ in the given phrase. It is common in .english to say both “do you want some sugar?” and to say “You want some sugar?” So why is what I wrote incorrect?
"dello" is the contraction of "di" + "lo" and normally it's translated as "of the" but not with this sentence. If you do a direct translation you get "you want of the sugar". That doesn't make sense and the reason why is because "dello zucchero" is an idiomatic expression. So as far as I have come to understand, the contraction of "di" and the articles "il", "la", "le", "lo" and "i" that are in front of a noun can either mean a vague amount of that noun (dello zucchero, degli uomini, del paninio, delle ragazze...,etc) or it takes the possessive and that noun owns the referring noun (il ragazzo ha i libri delle donne).
Btw, "from" is more often "da" than anything else.
Just in case you guys didn't know, idiomatic means: an expression of phrase that doesn't mean what it says. So like the English phrase, "you're being a hot dog". Your obviously not a real hot dog because that is a food item. So what this expression means is that you're showing off to impress people.
I also read this as "Are you desirous of the sugar?" Though we would be more likely in English to say "Do you want the sugar?" which is how I responded. But apparently that latter construction is not accepted. They seem to be teaching the idiom "dello" meaning "some" and don't want us to try alternative constructions.
The reason why it's wrong is because there is already a word for "would you like" and it's "vorresti"; the singular form is "vorrei" or "I would like". Unless it's an idiom, more often than not, Duolingo wants a straight translation. So "vuoi dello zucchero?" simply means "you want some surgar?". If it was "would you like some sugar?" it would be something along the lines of "Vorresti un po 'di zucchero?" -> "would you like a little bit of sugar?".