Translation:Where do we go for dinner?
I think the reason that this translation wasn't acceptible is because firstly, the sentence in your translation should be "我们应该到哪儿吃饭“. But what your sentence implies to me as an English speaker is that you're asking the other person the equivalent of "where do you want to eat?" When this sentence is asking, "where do we go to eat". It's more literally asking for a physical location to eat at like a cafeteria or restaurant.
Also, "Where shall we go to for dinner?" should be accepted. I think that while the focus is on the Chinese, it's still useful to point out other, equally valid, English translations. That way, learners are less frequently frustrated by having to conform to an overly rigid correct answer.
去 means to go. 走 means to walk. 到 means to arrive.
It seems that a lot of times you can translate all of them as to go in English but from what I got so far, 到 is always strongly related to the destination place like the sentence "到你的学校怎么走", while 走 is closely related to the path or the actual movement, like in "走吧" (let's go, let's walk, let's move)! On the other hand, 去 seems to be the actual "leave the current position", the actual "to go". "今晚我去上海".
Cagprado explained it pretty well. 到 can be used by itself, but you'll often see it used w/ 去 to form a grammar pattern, like "到 location 去 do an action", for example: "我们到电影院去看电影," "we go to the movie theater to see a movie." You can also use 到 to say that you did something, for example: "我看到，听得到， 来到美国, etc." "I saw, I hear/heard, I arrived in America". As for 走, cagprado did the best at explaining this. It's the physical action of walking or used when asking someone how to walk to a place from where you are, like when asking for directions, for example " 从这儿到银行怎么走" "How do I get/walk to the bank from here" or "你去哪儿怎么走" "How do I walk there". Both examples used 到 and 去 in conjunction w/ 走.
I think many of the posters are trying to justify their misunderstanding of the Chinese and the subtle difference in meaning between 到 and 去in the context of this sentence. "Where shall we go for dinner" might be understood in the context of the situation, but if being properly accurate the program has provided the accurate English translation. This sentence is enquiring as to where the location is for dinner in terms of a routine location. E.g. a newly arrived student in a hostel, or newly arrived guests in a hotel would be asking "Where do we go for dinner?" seeking clarification of where guests would routinely have their dinner while resident at that hostel, hotel, or wherever. In terms of "Where shall we go for dinner" if asking specifically about where they might go for dinner tonight, or tomorrow night, or any other time in the future the sentence would be "我们去哪儿吃晚饭". This would imply, for example, that last night we wnt to Wang's Restaurant for dinner, so where will we go for dinner tonight.
You have come up with a good context in which the current default English with "do" is acceptable. But I doubt it's what the people who added the question to course had in mind given how much hokey English is still in the course. (And hokey Chinese from what I read in the comments from native Chinese speakers.)
I am confused by the subtly different English translations! "Where do we go for dinner?" is context specific; it's a phrase used by people new to a place (eg school, workplace) to ask where they must go for dinner. "Where should we go for dinner?" more often indicates a choice. Both seem to be acceptable answers here. Is that really the case in the Chinese?
In the app, the only possible translation given is 'where do we go for dinner.' This is a slightly weird construction in English, as it implies that going for dinner is a repeated action and the location is the same place every day, but the speaker doesn't know where that is. Would 'where are we going for dinner?' (which means that dinner at the particular unknown location could be a one-off action) also work?
I think your translation is one of many correct possibilities. You should report options like this and choose the "I think my answer is correct" option. If there is no reason your translation can't be accurate they can add it to their options so it provides a benefit to other users.