You have a point - there will need to be a lot of explanation for grammar in this course... You should remember, though, that this course is still being fleshed out. It has only recently been put out for beta testing.

You should take a look at Tae Kim's guide. It's what I've been using for grammar so far.

I agree in part, knowing team will improve it with our feedback. On the other hand, these quirks make it interestingly similar to how we humans learn: a game challenge, putting the pieces of the puzzle together.

Yep. Common mistake. Don't make Japanese conform to an English way of thinking. The results can be really bad...

The sentence structure is like this: どれ (which) を (indicating OBJECT - In this case どれ) 食べます (verb meaning "to eat") か (indicates question).

tabe is the root word, tabemasu is the full verb.

Japanese had no future tense. It's implied from context.

を is for the direct object of the sentence and は is the topic particle (which is omitted in this sentence)

Yes, like [neko wa kuroi] (the cat is black), [omae o shinjiru] (believe in yourself).

I think that's precisely the point of this exercise.

In Japanese, どれ is used when you have a finite selection to choose from, whereas 何 is used in more broad and general situations where the possible answers are unbounded by what is in front of you.

You're exactly right that, in particular situations, they could be used interchangeably for what/which, but generally speaking, "which" tends to better convey the idea behind どれ, and "what" is better for 何

Dore..for the known. Nani...for the unkown.

I'm still learning, but I think "ing" verbs are usually treated differently. Like "eating" =/= "eat" or "will eat." Aren't "ing" verbs usually expressed in Japanese using て form + いる? Again, still learning...

I typed "which one will we eat?" and it was correct. I think it doesn't matter as long as it's more than one person. Duolingo tends to count "I" incorrect if "Watashi" is not used in the sentence. In the real world, it would depend on what was said earlier to know the definite meaning of the sentence. I think you're techinically also correct, but I'm not a native speaker so I can't be entirely sure.

I guess japanese people have other ways to question themselves. Like in english you won't really say "What am I eating?" but rather ask yourself or someone else "What is that?"

It is from context. If there is no context, most probably "you" if it is a question, and "I" if it is a plain sentence.

It is pronounced. In the verb 食べます, 食 is pronounced as た. Since the kanji is part of a word which has okurigana (meaning hiragana or katakana which is a necessary part of the word), it uses its kun'yomi た, instead of its on'yomi しょく.

By making yourself the subject on the sentence. I.e., (Watashi/Boku wa) dore o tabemasu ka? This sentence assumed it was being asked of someone, so context meant the "Which one to eat?" Turned into "Which one will you eat?" Which, fully wrote out, I believe is anata wa dore o tabemasu ka?

Either "do you" or "will you." Japanese simple tense is either English simple present tense or simple future tense.

Yes, I can understand your frustration. Unfortunately because this course doesn't seem to be fully finished yet, there isn't any good explanation of a lot of the unspoken things in Japanese. The problem is that a huge part of Japanese language is tied up with Japanese culture.

The reason we can assume you are not asking a question to yourself is because the sentence uses ます. ます, and です for that matter, are forms used to show politeness and showing politeness to yourself is considered incredibly self-absorbed and somewhat faux pa in Japanese culture. Also due to this politeness factor, "which to eat" or "which one to eat" are, while not incorrect, not good translations.

Also, "which one should I eat" has a slightly different meaning, even in English, from "which one will I eat" and likewise has a different translation.

食（た）べる=eat 飲（の）む=drink

No. どれ is a question word where the speaker is asking the listener to choose one of the several choices. Therefore "which one" is a more appropriate translation over "what."

Edit: To say "want to eat," it would be 食べたいです

The simple form 食べる/食べます means eat or will eat depending on context. It has been answered in this thread before.

Yes, it's very common, although it's generally avoided in formal writing. As you pointed out, か is used to indicate a question, but in my opinion, it does this mainly grammatically. From my experience, the question mark is used to show question-like intonation, particularly in informal writing, where using か can sound blunt or harsh.

That's usually the intention behind saying this sentence, but it doesn't actually mean that.

Compare this sentence with a simpler yes/no question version, for example ごはんを食べますか？ which means "Do you eat rice?" or "Will you eat rice?" The former asks about whether rice is eaten, as a general principle or a habit, and the latter asks about whether rice will be eaten, at some unspecified time in the future. Neither of these ask about whether eating rice is a preference or a desire, which is what "want" refers to.

Sure, "Will you eat rice?" usually has the implication of "because I will make it for you, if you want", but that implication is not the same as actually saying "Do you want rice?"

Exactly the same rules apply to the case of どれを食べますか？ which becomes either "Which (one) do you eat?" (as a habit or on general principle) or "Which (one) will you eat?" (whether you want to or not).

Yes, it can. As has been mentioned many times before, 食べます can mean "eat" or "will eat", so since "going to eat" in this case is synonymous with "will eat", it should be fine.

これ (this one)

or

これを食べます (I will eat this one)

Context. Japanese relies heavily on context for many things.

It depends on the situation. We often use "are eating" when we actually mean "are going to eat." In this case, this is similar to "will eat" and we use 食べます or 食べるつもりです. If we mean "already eating," then the correct form is 食べています.

は is used for promoting a part of a sentence to the topic. を is for indicating a noun is the direct object of a verb.

All question words cannot be promoted to a topic, so it is wrong to use は in this sentence.

"Which" itself is どの and it is followed by a noun, e.g. どの本= which book. （この/その/あの/どの this/that/which something）

"Which one" is どれ （これ/それ/あれ/どれ this/that/which one）

Which direction is どっち or どちら （こちら/そちら/あちら/どちら this/that/which direction） This is also used as a polite substitution of どれ, so you can say どちらをたべますか

It is the same sentence どれを食べますか and you can add the optional subject into the sentence to clarify e.g. 彼はどれを食べますか "Which one does/will he eat?"

yes

食べ is a verb. The question would be 水は何ですか

To form a complete sentence in English, either "which one do you eat" or "which one will you eat." Japanese simple tense can mean present or future tense depending on context.

It is asking for which one (どれ) and not a yes/no question.

It's in there for me. In this sentence, 食 is pronounced ta as part of the verb 食べます tabemasu

In English? "Want to eat" has more of a sense of immediacy, whereas "prefer to eat" feels more general.

To convey that nuance in Japanese is a bit beyond the scope of this course I think, but "What do you want to eat" would be 何を食べたいですか？ and "What do you prefer to eat" would be 食べるのは何が好きですか？

Because "what" is different from "which one." "Which one" implies that there are several choices to choose from. In Japanese, "what" is 何（なに） and "which one" is どれ. Please refer to the other comment in this thread as well as it has already been answered.

Yes, it's incorrect, for a couple of reasons. Firstly, どれ means "which", not "what". In certain situations, what/which could be used interchangeably, but generally speaking, "which" tends to better convey the idea behind どれ, and "what" is better for 何, so I can appreciate why Duo keeps the translation strict in these learning exercises.

Secondly, and more importantly, "can eat" has a vastly different meaning from "will eat". In your suggestion, the speaker is asking either what things are edible/able to be eaten or what things are permitted to be eaten. Both of these differ from the actual meaning of which things do you intend to eat, and accordingly have different verb conjugations associated with them.

Yes you have. If you were at a bakery and got some donuts with your friend to share and you sit down to eat them then your friend could say "Which one will you eat?" It is correct English grammar and keep in mind that it is almost always impossible to compare English grammar/structure to Japanese.