Could you tell me ____ ? ?

In English we distinguish between two types of questions: direct questions (where we invert subject and verb) and embedded questions (where the question is part of a larger sentence, so we keep the normal subject–verb order).

1. Direct question form
If you want to ask someone directly, you say:
What time is it?
Here, the verb “is” comes before the subject “it,” which is the usual pattern for a direct, stand-alone question.

2. Embedded question form
When you embed that same question inside a larger sentence introduced by phrases such as “Could you tell me…?”, you no longer invert the subject and the verb. Instead you use the statement order (subject + verb). So the embedded form becomes:
what time it is
That way the full sentence reads:
Could you tell me what time it is?

Why the other choices are unsuitable:
- “What’s the time?” is a shortened direct question, and although it’s perfectly natural by itself, it still uses inversion (and a contraction) and cannot be embedded without changing its word order.
- “What time is it?” is the full direct question; again, inversion makes it wrong inside “Could you tell me…?”
- “What it is time” scrambles the normal order and the position of “time,” producing an ungrammatical phrase.

Only “what time it is” follows the rule for embedded questions (keeping subject before verb) and slots correctly into “Could you tell me ____?”

Summary: In an embedded question we maintain statement order (subject + verb), so “Could you tell me what time it is?” is the grammatically correct form.