for example: what is the difference between "Where America is?" and "Where is America?" ?


"Where America is" is not grammatical as a question. In a question with a WH word ("who", "what", "where", "why", "how" etc) we always invert - put the auxiliary (or the verb if it is "be" or sometimes "have") before the subject.*

When we embed the question in a larger sentence, then we don't invert:

Ask him where America is.

[* For yes/no questions, without a WH word, inversion is required in formal language, but optional in colloquial speech: "Did you go?" or (informal) "You went?"]

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