When you ask "Where is the book?"
Are both answers ("It is nowhere.") in Japanese correct?
Is 「どこにもありません。」the same as 「どこもではありません。」, are both correct?
どこにもありません is correct, but どこもではありません is quite strange, I have never heard it.
The verb ''ある'' which means ''exist'' is usually used with a particle ''に''
E.g. In response to '本はどこにありますか。':
On the other hand, ''ある'' with ''で'', which means that someone or something is the same as the subject of the sentence, is quite similar to ''です''. This meaning of ''ある'' is rather used with ''は'' in negative sentences.
E.g. In response to '本はどこですか。':
※ 'あそこであります' isn't wrong, but is quite an old-fashioned expression in positive sentences.
By the way, these are three hints that might help you:
はdoesn't come with interrogatives like どこ, なに, いつ, だれ and so on.
はdon't come together.
はnever comes before
まで, etc. That is a reason why どこもではありません is very strange.
You can say the following:
Reading my explanation above, you may wonder if どこでもありません is correct.
Although people DO say どこでもありません in some cases, it is NOT appropriate for the reply to 本はどこですか／どこにありますか。
I am very sorry but I can't explain the reason well...
The simple answer to the question, 「本はどこですか？」is this;「本がない。」(There is no book, The book isn't there). But however, you are asking about if「どこにもありません」and「どこもではありません」. As someone above has said, 「どこもではありません」is completely wrong. However, the first one can be retrofitted to make more sense. Though it does make some sense, it is not very good and sounds queer and unnatural. I think to correct the sentence to make it sound more natural, it should be like this:「何処にもない」(doko ni mo nai) to say "it is not anywhere", or, "is not to be found anywhere", or is, "nowhere to be found". I hope I was helpful. Have fun learning Japanese! (⌒▽⌒)