هذا ابني.

A simple learner pronunciation is hādhā ibnī.

• هذا = hādhā
• ابني = ibnī

A few pronunciation notes:

• dh here sounds like the th in this, not the th in think.
• The ā is a long vowel, so hold it a little longer.
• ابني means my son.

In careful grammar, ابن begins with a special kind of hamza, so in fully connected formal pronunciation the initial i can weaken or drop. But for a learner, hādhā ibnī is a perfectly useful way to say it.

The sentence has two parts:

• هذا = this
• ابني = my son

And ابني itself breaks down into:

• ابن = son
• ـي = my

So literally, it is this my son, which in natural English is This is my son.

In Arabic, the present-tense verb to be is usually not said in simple sentences like this.

So:

• هذا ابني literally looks like this my son
• but it means This is my son

This is very normal in Arabic.
If you wanted a past meaning, Arabic would use a verb, for example with كان for was.

هذا is the demonstrative meaning this for a masculine singular noun.

Since ابن (son) is masculine singular, هذا is the correct choice.

Compare:

• هذا ابني = This is my son
• هذه ابنتي = This is my daughter

So yes, the demonstrative matches the gender of the noun.

Because Arabic often shows possession by adding a suffix directly to the noun.

Here:

• ابن = son
• ابني = my son

The ending ـي means my.

This is very common in Arabic:

• كتابي = my book
• بيتي = my house
• أخي = my brother

So ابني is not two separate words; it is one word meaning my son.

Because a noun with a possessive suffix is already definite.

So Arabic does not say:

• الابني for my son

Instead, it says:

• ابني

That is because my son is already specific. The suffix ـي makes it definite.

Yes. هذا هو ابني is also grammatical.

• هذا ابني = simple, natural This is my son
• هذا هو ابني = This is my son, but with a little more emphasis or clarity

For a beginner, هذا ابني is the basic form to learn first.

A fully vowelled version is usually written:

هٰذَا ابْنِي

This helps show the pronunciation more clearly:

• هٰذَا = hādhā
• ابْنِي = ibnī

In normal everyday writing, Arabic usually leaves these short-vowel marks out, so you will most often see:

هذا ابني

Yes. It is a nominal sentence: a sentence that does not need a verb in the present tense.

Very roughly:

• هذا = the topic / subject-like part
• ابني = the predicate / the information about it

So the structure is:

• this
  • my son

which Arabic uses to mean:

• This is my son

This pattern is extremely common in Modern Standard Arabic.

It is common, but learners often notice that it behaves a little differently in pronunciation and spelling.

A few useful points:

• The basic word is ابن = son
• When you add ـي, it becomes ابني = my son
• The word begins with a special hamza type, so its initial vowel is not always pronounced the same way in connected speech

You do not need to master all of that right away. For now, the important thing is:

• ابن = son
• ابني = my son

You would change the demonstrative.

• هذا ابني = This is my son
• ذلك ابني = That is my son

So the part that changes is هذا → ذلك.
The word ابني stays the same.