لا شك لدي.

Because Arabic often uses verbless (nominal) sentences in the present tense.

So لا شك لدي literally works like:

• No doubt
  • with me / for me

The idea of there is is understood automatically. So the full sense is:

• There is no doubt for me
• more naturally in English: I have no doubt

Arabic does this very often, so a verb is not needed here.

Here لا is not just the ordinary no/not. It is the special grammar particle called لا النافية للجنس, often translated as there is no... whatsoever.

In this sentence, it gives a strong general negation:

• لا شك = no doubt at all

So it is stronger and more idiomatic than simply negating a verb.

After this kind of لا, the noun is normally indefinite, not definite.

So:

• لا شك = no doubt
• not لا الشك

Using the indefinite noun gives the broad meaning no doubt of any kind.

That is why شك appears without الـ.

In fully vowelled Arabic, this would be:

• لا شَكَّ لدي

After لا النافية للجنس, a simple singular noun like شك is treated in a special way: it is built on fatḥa.

So you get:

• شَكَّ
• not شَكٌّ
• and not usually شَكًّا in this construction

In normal unvowelled writing, all of those short vowels are omitted, so you just see:

• شك

لدي means something like with me, for me, or in my possession / in my view, depending on context.

In this sentence, it means:

• for me
• from my side
• idiomatically: I have

So:

• لا شك لدي = I have no doubt

It is a very common formal way to express possession or personal certainty.

It comes from لدى plus the pronoun ـي (my / me).

So the fully vocalized form is:

• لَدَيَّ

It is commonly pronounced:

• ladayya

And the whole sentence is pronounced approximately:

• lā shakka ladayya

In ordinary unvowelled writing, you usually see it simply as:

• لدي

Both can often mean I have or with me, but they are not exactly the same in tone.

• لدي is usually more formal, written, or Modern Standard Arabic
• عندي is very common too, but often feels a bit more everyday or closer to spoken usage

So:

• لا شك لدي sounds polished and standard
• ما عندي شك would be much more colloquial in many dialects

In MSA, لدي is a very natural choice here.

Yes. ليس لدي شك is correct and means almost the same thing:

• ليس لدي شك = I do not have any doubt
• لا شك لدي = I have no doubt

The difference is mostly one of style:

• لا شك لدي is more idiomatic, compact, and often a bit stronger or more elegant
• ليس لدي شك is straightforward and clear

Both are good MSA.

Sometimes yes. Arabic often leaves the object of doubt understood from context.

For example, a fuller sentence could be:

• لا شك لدي في ذلك = I have no doubt about that
• لا شك لدي في الأمر = I have no doubt about the matter

But if the context already makes it clear what is being talked about, لا شك لدي by itself is completely natural.

It is definitely Modern Standard Arabic and sounds natural in:

• writing
• news
• formal speech
• essays
• serious conversation

In casual spoken dialects, people often prefer other expressions, such as forms meaning I don't have any doubt with عند or a dialectal negative pattern.

So this sentence is very useful to learn, especially for reading and formal Arabic.

The sentence starts with the core idea:

• لا شك = no doubt

Then it adds whose perspective this is:

• لدي = for me / with me

That order is natural in Arabic. It presents the state first, then the person connected to it.

So Arabic is not literally saying I no doubt have. It is more like:

• There is no doubt, as far as I am concerned

That is why the structure may feel different from English, even though the meaning is simple.