Choose the most suitable option to replace the highlighted part of the sentence:
No one knows where is he staying.

The correct option is where he is staying.

Detailed Explanation:

In English grammar, when a question (e.g., "Where is he staying?") is embedded inside another main sentence (e.g., "No one knows..."), it becomes a noun clause or an indirect question.

Unlike direct questions, indirect questions use statement word order (Subject + Verb) instead of question word order (Verb + Subject).

Let's compare the word orders:

• Direct question format (Inverted order): Question word + Auxiliary verb + Subject + Main verb
Example: Where is he staying?

• Indirect question / Embedded clause format (Statement order): Question word + Subject + Auxiliary verb + Main verb
Example: ...where he is staying.

Therefore, inserting the direct question structure "where is he staying" into the sentence creates a grammatical error. The verb "is" should follow the subject "he".

Replacing the highlighted phrase gives the correct, grammatically sound sentence:
"No one knows where he is staying."