Я пока ещё не знаю, какое сегодня число.

Here пока ещё means something like for now / as of now / still / yet.

So Я пока ещё не знаю... means:

• I still don’t know...
• I don’t know yet...
• For now, I don’t know...

A useful point: пока has several meanings in Russian, but here it does not mean while. In this sentence, it gives the idea of a situation that is true at the moment.

Yes, they overlap a bit, but together they sound very natural in Russian.

Compare:

• Я не знаю = I don’t know
• Я ещё не знаю = I don’t know yet / I still don’t know
• Я пока не знаю = I don’t know for now / at the moment
• Я пока ещё не знаю = a slightly fuller, conversational way to say I still don’t know yet / for now I still don’t know

So the combination adds a sense of not knowing at this point in time, but maybe knowing later.

Because какое agrees with число, and число is a neuter singular noun.

Forms of какой:

• masculine: какой
• feminine: какая
• neuter: какое
• plural: какие

Since the phrase is какое ... число, the question word must also be neuter singular.

It usually does mean number, but in this expression it means the day of the month, that is, the date.

So:

• Какое сегодня число? = What’s today’s date?

Literally, it is closer to What number is it today?, but English does not say it that way. In Russian, this is a normal everyday expression.

Yes, very much so. It is one of the standard ways to ask for the date.

It specifically asks for the date/day of the month, not the day of the week.

Compare:

• Какое сегодня число? = What’s today’s date?
• Какой сегодня день? = What day is it today? / sometimes What day of the week is it today?

So if you want Monday / Tuesday / Wednesday, use день.
If you want the 5th / the 24th / the 31st, use число.

Because Russian normally omits to be in the present tense.

In English, you say:

• What is today’s date?

In Russian, the present-tense is is usually not said:

• Какое сегодня число?

The same thing happens in many simple sentences:

• Он врач = He is a doctor
• Сегодня понедельник = Today is Monday

So the missing verb is completely normal.

Because какое сегодня число is a subordinate clause, specifically an indirect question.

Compare:

• Direct question: Какое сегодня число?
• Indirect question: Я не знаю, какое сегодня число.

In Russian, subordinate clauses are usually separated by a comma, and that includes indirect questions after verbs like:

• знать = to know
• спрашивать = to ask
• понимать = to understand
• помнить = to remember

So the comma is required here.

Yes, Russian word order is flexible, but some orders sound more standard than others.

The most natural version here is:

• какое сегодня число

You may also hear:

• какое число сегодня

Both are understandable, but Какое сегодня число? is the most common set phrase.

In the main clause, too, some variation is possible:

• Я пока ещё не знаю...
• Пока ещё не знаю... (dropping я if the subject is clear)

Russian often omits я when it is obvious from context.

Because with verbs, не is usually written separately.

So:

• не знаю = don’t know
• не понимаю = don’t understand
• не помню = don’t remember

This is the normal rule. There are some exceptions in Russian spelling, but знаю is not one of them, so не знаю must be written as two words.

Because Russian often places time words where they sound most natural rhythmically, and in this expression the usual order is:

• Какое сегодня число?

Here сегодня helps specify today’s date, and this middle position is idiomatic.

English learners sometimes want a one-to-one structure like What date today is?, but Russian is not copying English word order. The phrase works as a whole.

Usually with a neuter ordinal number, because it matches the implied число.

Examples:

• Сегодня пятое. = It’s the fifth today.
• Сегодня двадцать четвёртое. = It’s the twenty-fourth today.
• Сегодня пятое мая. = It’s May fifth.
• Сегодня двадцать четвёртое апреля. = It’s April twenty-fourth.

A short answer without the month is very common if the month is already clear.

Yes, you can, and it means almost the same thing: What’s today’s date?

But there is a slight difference in feel:

• Какое сегодня число? = the most standard everyday expression
• Какая сегодня дата? = also correct, but often feels a bit more formal or explicit

So for normal conversation, Какое сегодня число? is usually the phrase learners hear first.

Because the subject is я.

The verb знать in the present tense is conjugated like this:

• я знаю = I know
• ты знаешь = you know
• он/она знает = he/she knows
• мы знаем = we know
• вы знаете = you know
• они знают = they know

So Я пока ещё не знаю... means I still don’t know... exactly because знаю is the I form.