Translation:What grade are you in?
In East Asia, there are no grades sitting together in universities, but there are grades as implicit identities.
Perhaps astonishing to you, in universities in East Asia, a lower-grade student is expected to obey their higher-grade fellows, and the higher-grade is somehow in charge of 'educating' and taking care of lower graders.
For example, I have a T-shirt as a souvenir of entering the university in 2006. Before 2009, unless required (as in some activities), I kept it in my wardrobe; but after 2010, I wore it almost every day in summer. When I was a lower-grade graduate student, I listened to and used honorific addressing to higher graders, but I did not need to pay when all the students in the lab dined out; when I was in my final year, I paid (the payroll evenly divided among the final-year students) the dinners. Though I am not Japanese, in Japan this is more intensive.
In Africa it Applies but in Elementary, Middle and High school, so when I came to the US and I meet a senior student I mistakenly say e.g. "Senior John" or Senior for short but then I learnt it does not apply in the US so yeah pretty similar except in some Universities in Africa, it is best to stay on your on or with people you knew before you entered university, if you do not want to bring trouble upon yourself.
It is possible that we can be referring to the level of the material we are looking at.
"this math test is hard." "what grade level is it?" Although it is not the most effective it is still possible.
Also, although my Japanese sucks. I'm sure there is a way to add these pronouns rather than making it this vague.
Actually, 年生 doesn't quite work like that.
As some other comments have pointed out, while in English, we can use "grade" in a few different ways even in a school setting, the Japanese word 年生 refers strictly to "students" because it has 生 in it. You could even think of it as a kind of suffix which means "student", e.g 中学生 = "middle school student", 留学生 (りゅうがくせい) = "study abroad student", 一年生 = "one/first year student", 先生 = "(studied) ahead of you student", etc
"Grade" in the way you've used it in your example would be 学年 in Japanese, and "grade" to describe your results for that test would be 成績 (せいせき).
There are definitely ways to make this sentence less vague by adding pronouns, but just like picking which translation of "grade" is most accurate, you have to consider how Japanese people would say what you want to say in the same situation. Grammar problems aside, you can't simply switch out each English word for the Japanese equivalent and expect the result to sound correct or natural. When it comes down to it, you just have to get used to the idea that pronouns are omitted very often in Japanese.
In British English we say year not grade. I translated this as "what year are you in? " and it was correct . You can see that the meaning of nensei is yeargroup for students, therefore it can only apply to students not study materials or anything else. Just as you don't say in English "what year group is this test?" you don't say nensei either .
This needs some explaining better. I'm a third-year student and I have not heard that I'm not that is something bad to say in certain situations. I'm aware of that most Japanese don't use it, as we foreigners learn at a point that many words start disappearing in Japanese conversation. However is it really bad to say anata ha? Needs clarity.
saying ''anata'' is better to be omitted as it can come off as rude. Obviously, since you are a foreigner they won't be insulted but better leave it out all together. (it litterally means ''over there'' and when Japanese use it it's most of the time someone talking to their husband.)
The thing is the proper way to directly addressing someone is by using his name or title.
Using a generic pronoun means that either you forgot his name or title, or you don't care.
That is what may be rude.
There should have been first a presentation (はじめまして、マルマルです。よろしくおねがいします。) and the other person would also said his name, and thereafter you are supposed to address him/her by the name, not あなた.
It would be better,I think, if you forgot the name, to humbly ask the name again first, rather than don't caring and going withあなた.
This is a really interesting question, which I had to look up too. I found this great explanation on Tofugu https://www.tofugu.com/japanese/onyomi-kunyomi/
Essentially, your guess was pretty close. The "gaku" reading comes from another form of Chinese that was predominant during the Wu Dynasty, whereas I believe modern Mandarin stems mostly from the Han Dynasty, from which many Japanese on'yomi are also derived.
"Nen" is year in a general sense. For example, if it was "nan ne desuka?" it is like "what year is it?" (or "What year are we in?"). As for, "Nensei" it means "school year/grade" referring to people (the students), so it's not applied to not objects like "first-year content".
Duolingo seems to be strict on prepositions, even though it's not about へ or に -- even English prepositions exclusive to English, e.g. "I'm IN ...th grade" seems to be stressed about even though the Japanese equivalent doesn't use a preposition. This seems like it's unnecessary to put an "if answer is exactly as the translation, correct it" logic gate in this question.
Just to be clear, へ or に don't strictly need to correlate to a preposition in the English translation, and vice versa, prepositions in English don't necessarily need to include a particle in Japanese. It often does correlate well, but in cases like this, judging the correctness of a translation requires understanding common usage in both languages.
However, Duo isn't a program for translating; it's a program for learning. At this point, it's even still in Beta for this course, so acceptable answers, like "What grade are you?" (standard Australian English), may not be fully set-up yet.