Sabihin po ninyo kung kailan darating ang nobela.

Yes. In this sentence, sabihin is being used as an imperative, so the whole opening Sabihin po ninyo... means something like Please tell...

This pattern is very common in Filipino:

• Sabihin mo = tell
• Sabihin ninyo = tell, addressed to more than one person or to one person politely

So even though sabihin can also appear in other grammatical contexts, here it functions as a polite command/request.

Po is a politeness particle. It adds respect and makes the sentence more courteous.

So:

• Sabihin ninyo... = Tell...
• Sabihin po ninyo... = Please tell... / Tell..., respectfully

It does not change the basic meaning very much, but it changes the tone. Native speakers use po when speaking politely, especially to elders, strangers, customers, or people of higher status.

That is because Filipino uses different pronoun sets depending on the grammatical structure.

In this sentence, after the verb sabihin, the pronoun appears in the genitive/enclitic form:

• mo = you, singular
• ninyo = you, plural or polite singular

So:

• Sabihin mo = tell
• Sabihin ninyo = tell, you all / tell, sir/ma’am

By contrast, kayo belongs to a different pronoun set. You can use kayo in other sentence patterns, but after this kind of verb form, ninyo is the normal choice.

It can be either:

• plural: speaking to more than one person
• polite singular: speaking respectfully to one person

That is very common in Filipino. So Sabihin po ninyo... could be addressed to:

• several people, politely
• one person, politely

Context tells you which one is meant.

Here kung introduces an embedded or indirect question.

Compare these:

• Kailan darating ang nobela? = When will the novel arrive?
• Sabihin po ninyo kung kailan darating ang nobela. = Please tell when the novel will arrive.

So kailan by itself is when, but in a longer sentence after a verb like tell, know, ask, or remember, Filipino often uses kung to introduce the question clause.

In this sentence, kung kailan darating ang nobela means when the novel will arrive.

Darating is the future or contemplated aspect of the verb meaning arrive.

Related forms are:

• dumating = arrived
• dumarating = is arriving / arrives regularly
• darating = will arrive

So kailan darating ang nobela means when the novel will arrive.

Because ang nobela is the topic/subject of the clause darating ang nobela.

With a verb like darating meaning will arrive, the thing that arrives is marked with ang:

• Darating ang nobela. = The novel will arrive.

If you used ng, it would signal a different grammatical role, and it would not fit this sentence.

So in this clause:

• darating = will arrive
• ang nobela = the novel, as the subject/topic

Filipino commonly uses verb-initial word order, especially in neutral sentences.

So instead of following the usual English pattern subject + verb, Filipino often starts with the verb:

• Darating ang nobela.
• literally: Will arrive the novel

Likewise:

• Sabihin po ninyo...
• literally something like: Tell, please, you...

This is normal Filipino sentence structure, not a special or unusual arrangement.

Sometimes yes, if the context already makes the addressee clear.

For example, people may say:

• Sabihin po kung kailan darating ang nobela.

But including ninyo makes the sentence clearer and often sounds more complete. In polite requests, keeping the pronoun is very natural.

No. The whole sentence is a request, not a direct question.

The direct question inside it would be:

• Kailan darating ang nobela? = When will the novel arrive?

But the full sentence is telling someone to provide that information:

• Sabihin po ninyo kung kailan darating ang nobela.

So the main sentence is imperative, while kung kailan darating ang nobela is an embedded question.

Yes, that is a very natural translation.

Depending on context, Sabihin po ninyo kung kailan darating ang nobela could be rendered as:

• Please tell me when the novel will arrive.
• Please let me know when the novel will arrive.
• Kindly tell me when the novel will arrive.

The exact English wording can vary, but the Filipino structure stays the same.