In what context would this be encountered? Does this refer to a discount in a shop for example?
It sounds awkward and I can't think of any use for it. I guess it's just one of those meaningless phrases typical of Duolingo.
I had the same question. Could it be regarding e.g. an new interest for a bank account or say the support of a political party in a poll?
No, if you talk about percentages in those contexts you'd have to use words like interest rates ('Zinsraten') and votes ('Wählerstimmen'). Kueckauer is right, there is absolutely no use for this phrase in German.
It could be used when examining data. Like, that percentage of population growth is a new figure.
I don't think anyone would say "das Prozent". I'd use something like "der Wert" (the value).