أنا لا أعرف كل الجيران في هذا المبنى.

أنا is optional.

Arabic verbs usually show the subject in the verb form itself, and أعرف already means I know. So you can say:

لا أعرف كل الجيران في هذا المبنى.

Adding أنا can make the subject clearer or more emphatic, especially if you want contrast, such as I do not know them, but someone else does.

لا is the normal way to negate a present-tense or general imperfect verb in Modern Standard Arabic.

• أعرف = I know / I am knowing
• لا أعرف = I do not know

So the structure is very straightforward:

أنا + لا + أعرف

A learner might wonder about ليس, but ليس is mainly used to negate nominal sentences, not a verb like أعرف in this kind of sentence.

Arabic often distinguishes between two kinds of know:

• عرف / يعرف = to know, be acquainted with, recognize
• علم / يعلم = to know information or facts

With people, عرف is usually the natural choice. Since neighbors are people, أعرف fits well.

So:

• أعرف الجيران = I know the neighbors
• أعلم الجواب would sound odd for I know the neighbors, because علم is more about factual knowledge

كل means all or every, depending on context.

Here, كل الجيران means all the neighbors.

So the sentence means:

I do not know all the neighbors in this building.

It refers to the whole set of neighbors connected with this building, not just neighbors in general.

Because the sentence is talking about a specific group: the neighbors of this building.

In Arabic, كل is often followed by a noun in an iḍāfa-like relationship:

• كل الطلاب = all the students
• كل الناس = all the people
• كل الجيران = all the neighbors

Using ال on الجيران helps show that this is a known, definite set, not just neighbors in general.

It most naturally means I don’t know all of them.

In other words, it suggests that you know some neighbors, but not every neighbor in the building.

If you want to say I don't know any of the neighbors, Arabic would usually say something more explicit, such as:

أنا لا أعرف أيًّا من الجيران في هذا المبنى.

So this sentence is about not the whole set, not necessarily zero neighbors.

The singular is جار = neighbor.

The plural جيران is a broken plural, not a regular sound plural.

So:

• جار = neighbor
• جيران = neighbors

This is very common in Arabic. Many nouns form their plural by changing the internal pattern rather than just adding an ending.

In Modern Standard Arabic, the normal order is:

demonstrative + definite noun

So:

• هذا المبنى = this building

That is the standard MSA pattern.

Some spoken dialects often use a different order, closer to the building this, but in MSA the standard form is هذا المبنى.

المبنى is pronounced al-mabnā.

The final ى is called alif maqṣūra. It looks like ي without dots, but here it represents a final long ā sound, not a y sound.

So do not pronounce it like mabniy.
It is mabnā.

This spelling appears in many Arabic words and can be confusing at first, but it becomes familiar with practice.

A fully vocalized version would be:

أَنا لا أَعرِفُ كُلَّ الجِيرانِ في هذا المَبنى.

Here is why:

• أعرفُ is the imperfect verb, so it is normally in the indicative: -u
• كلَّ is the direct object of أعرف, so it is accusative
• الجيرانِ comes after كل in an iḍāfa construction, so it is genitive
• في is a preposition, so the phrase after it is in the genitive environment
• هذا is indeclinable in form
• المبنى is a noun with alif maqṣūra, so its case ending is not visibly pronounced in the usual way

For many learners, the most important part here is noticing:

• كلَّ = accusative
• الجيرانِ = genitive after كل

Grammatically, كل is the direct object of the verb, and الجيران is attached to it as the second part of the construction.

So the structure is roughly:

• أعرف = I know
• كلَّ = all
• الجيرانِ = of the neighbors

That is why كل is accusative, while الجيران is genitive.

This is a very useful pattern to learn, because it appears often:

• قرأتُ كلَّ الكتابِ = I read the whole book
• أحبّ كلَّ الأصدقاءِ = I love all the friends

Yes, Arabic has some flexibility.

The most neutral version is probably:

لا أعرف كل الجيران في هذا المبنى.

You can also keep أنا at the front:

أنا لا أعرف كل الجيران في هذا المبنى.

That may sound a bit more explicit or emphatic.

You could also move the location phrase for focus, depending on context, but for a learner, the original order is very natural and safe.

In Arabic, when a demonstrative like هذا is used before a noun, the noun itself is normally also definite with ال.

So the standard pattern is:

• هذا الكتاب = this book
• هذا البيت = this house
• هذا المبنى = this building

Even though this already makes the phrase definite in English, Arabic still uses ال on the noun in this structure. This is normal and expected.