Are the following phrases exactly the same in terms of meaning? And are they
all correct in terms of grammar? Can I use them interchangably?

>   * tokyo e iku
>   * tokyo e iku n
>   * tokyo e iku no da
>   * tokyo e iku no desu
>   * tokyo e iku nda
>   * tokyo e iku ndesu
>

I know that, for example,

> tokyo e iku ndesu ne?

can be used to mean "you're going to Tokyo, right?" -- just to confirm what
you already know.

But I've heard "n desu" used in normal questions, where no confirmation is
seeking by one asking a question.

> nani o suru n desu ka?

Why is that?
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2017-02-03T05:40:58.403
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2017-02-16T06:05:08.853
2017-02-03T18:55:49.553
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question
questions no-da
Using verb + "n desu", "n da" in questions and in statements and with no confirmation
Basically, when you have an assumption about the response and are
_interrogating_ the other person, you append -n to the verb.

See [here](http://www.learn-japanese-adventure.com/how-to-use-n-desu.html) for
more information.
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2017-02-03T16:36:37.227
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answer
First of all, "no" and "n" are same. "no" can become n if there is no stress.

"no" is called 準体助詞, which makes a noun phrase from a sentence / an adjective.
It is just like "that" in English. "no" itself does not mean confirmation or
question. And, rather what comes after "no" adds these meanings.

~ndesu. It is that blah blah.

~ndesuka? Is it that blah blah?

~ndesune. It is that blah blah, isn't it?

Also, I want to note that ka at the last is sometimes omitted.
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2017-02-06T06:49:45.637
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東京へ行く and 東京へ行くんだ (which is essentially equivalent to 東京へ行くのだ) are quite
different in nuance. The first is merely expressing the proposition of going
to Tokyo. The second asserts that it is **the case of a situation of going to
Tokyo** , in a way similar to 本だ asserting that it is the case that something
is a book. Literally, it could be glossed as "It is that I/you/he are going to
Tokyo". Colloquially, assuming a bit of context, it could conceivable be
translated as "So you're going to Tokyo, huh."

With regard to なにをするんですか, the same applies. Whereas なにをしますか merely asks what
you are doing or will do, なにをするんですか again literally could be rendered as "What
is it that you are doing", which has the possible nuances, just like in
English, of "What on earth on you doing", or "Why are you doing that".
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