There are lots of ways to say this in English, but it seems to me that "When did you find out your score?" would surely be one of them. A: " I got a 96 on the math placement exam!" B:"That's great! I still don't know my results. When did you find out your score?" Duo disagrees with this, despite the mouse-hover listing "score" as one of the meanings for "Noten." :( I've reported this, but maybe I am wrong. Anyone see a problem with this translation?
(Native American English speaker) It sounds weird to say learnt- I've only ever heard that word used in literature. "When did you learn your grades?" sounds better, but still unnatural. "When did you find out your grades?" and "When did you get your grades [back]?" both sound perfectly normal
Learnt seems fine to me (Native British English speaker). "When did you learn your grades?" is perfectly fine and natural sounding to my ears, so it's likely one of those Anglo-American differences. "When have you learnt your grades?" is clumsy but should probably also be accepted as its meaning is clear and one shouldn't be punished for not being great at English when trying to learn German.
This seems somewhat vague to me as well, so I wouldn't mind a native speaker diving in either.
From what I can tell based on the PONS definition there are some things that don't work with von: etwas erfahren seems to mean to experience something, which doesn't seem to apply to von etwas erfahren (which seems to make sense). However they both seem to mean to learn of something: etwas erfahren apparently in the sense of hearing about "it" (zu hören bekommen), and von etwas erfahren in the sense of becoming aware of "it" (or details of "it") (Kenntnis erhalten). I think this means that the former is merely if you come to know of something from someone else, while the latter can be achieved by other means (e.g. "I was reading a book, and became aware of the Taj Mahal").
Dict.cc's definitions of etwas erfahren and von etwas erfahren seem to support this at least to some degree. However, they also list to come/get to know as a definition of etwas erfahren, although I think this is referring to people.
I could of course be totally off on this. Unfortunately, the German is Easy!/Your Daily German blog's entry (which is technically about Erfahrung but covers the related verbs and adjectives) isn't much help for once, although it does help differentiate the to experience something meaning from that of erleben.
Ich habe von dem Unfall gestern erfahren (Dativ, comes with the preposition) Ich habe erfahren, dass Du einen Unfall hattest. Ich habe diese Krankheit erfahren (personal experience) (Akkusativ)
I am a native speaker, but my knowledge of German grammar is far inferior to that of students of German. :-)
And I have a very hard time getting through this program because my answers are not based on what was taught before. Sigh.
It's in the past tense. A word-for-word translation would be "When have you your grades found out about?" The "Wann hast du… ?" translates directly as "When have you… ?", although in German the perfect doesn't have the same distinction of meaning as it does in English, so is just translated as "When did you… ?"
Assuming you mean "At what point in time must you check your grades?", and that the person you're talking to is singular and familiar (rather than plural (ihr), formal (Sie) or general (man)), I think that would be „Wann müsst du deine Noten überprüfen?“, although I'm not 100% sure überprüfen works for "check".
If you meant "Under what/which circumstances… ?" then I don't think I can help you there. It may well be that in German „wann“ = "under what/which circumstances" as "when" does in English, but I don't know one way or another.