أنت لا تعرف؟ بلى.

In Arabic, the verb تعرف already tells you the subject is you (masculine singular), so أنت is not strictly necessary.

• تعرف؟ = Do you know?
• أنت تعرف؟ = You know? / Do you know?

Adding أنت can give:

• emphasis
• clarity
• a slightly more direct or contrastive tone

So أنت لا تعرف؟ is a bit like saying You don't know?

لا is the normal particle used to negate a present/imperfect verb in Modern Standard Arabic.

So:

• تعرف = you know
• لا تعرف = you do not know

In this sentence, لا تعرف means you don't know.

Both verbs can relate to knowing, but they are used differently.

• عرف / يعرف often has the sense of to know, be familiar with, recognize
• علم / يعلم often has the sense of to know a fact, be aware, have knowledge

In many contexts, both can be translated as know, but تعرف is very common in everyday-style questions like this.

So أنت لا تعرف؟ is a very natural way to say You don't know?

Here, تعرف is second person masculine singular.

So the sentence is addressed to one male:

• أنتَ لا تعرف؟

If you were speaking to one female, you would say:

• أنتِ لا تعرفين؟

If short vowels are not written, the pronouns help show the difference:

• أنتَ لا تعرف؟ = to a man
• أنتِ لا تعرفين؟ = to a woman

A common pronunciation in MSA would be:

• ʾanta lā taʿrifu? balā.

A rough guide:

• أنت = AN-ta
• لا = lā
• تعرف = taʿ-ri-fu
• بلى = ba-lā

Notes:

• The ع in تعرف is a consonant that has no exact English equivalent.
• The final ى in بلى is pronounced like a long ā.

This is one of the most important points in the sentence.

In Arabic, بلى is used to reply to a negative question or negative statement in order to reject the negation.

So:

• أنت لا تعرف؟
• بلى. = On the contrary, I do know.

If you answered نعم to a negative question, it would usually mean you are agreeing with the negative idea:

• أنت لا تعرف؟
• نعم. = Yes, I don't know.

So:

• بلى = Actually yes, I do
• نعم = Yes, that's correct; I don't

Yes. بلى can stand alone as a complete reply.

That is very common when the meaning is clear from the question.

So this exchange works perfectly:

• أنت لا تعرف؟
• بلى.

The full implied meaning is something like:

• بلى، أعرف. = Yes, I do know.

But Arabic often leaves the rest unstated because it is obvious.

بلى does not match one single English word perfectly.

Its function is:

• to answer a negative question
• to cancel or reverse the negation

So in practice it often means:

• Yes, I do
• On the contrary
• Actually, yes
• No, that's not true
  (depending on what sounds most natural in English)

Its core meaning is: the negative statement is wrong.

Yes. You could simply say:

• لا تعرف؟

That would still mean Don't you know? or You don't know?

Adding أنت makes it more explicit and often more emphatic:

• لا تعرف؟ = neutral
• أنت لا تعرف؟ = You don't know?

Yes. This sentence is normal and understandable.

Arabic often allows flexibility in word order. Here you have:

• أنت = subject pronoun
• لا تعرف = negated verb phrase

So the structure is basically:

• You not know?

This is very natural in Arabic. In English, we usually need do:

• Do you not know?
• Don't you know?
• You don't know?

Arabic does not need an extra helping verb like do.

With full vowel marks, the sentence would be:

• أَنْتَ لا تَعْرِفُ؟ بَلَى.

This shows:

• أَنْتَ = you (masculine singular)
• تَعْرِفُ = you know

In normal Arabic writing, these short vowels are usually omitted, so you will usually see:

• أنت لا تعرف؟ بلى.

This sentence is perfectly fine in Modern Standard Arabic.

In everyday spoken Arabic, people often use dialect forms instead, and those vary by region. But for MSA, this sentence is short, correct, and natural.

So for a learner of MSA, the important thing is:

• the structure is correct
• بلى is the standard reply to a negative question when you mean actually, yes

Arabic uses a mirrored question mark:

• ؟

So:

• أنت لا تعرف؟

This is just the Arabic version of ?. Its function is exactly the same.