هذا يشبه صديقي.

هذا means this. It is the masculine singular demonstrative in Modern Standard Arabic.

You use هذا for:

• a masculine singular noun
• a male person
• something treated as grammatically masculine singular

If the thing were feminine, you would usually use هذه instead.

يشبه is the present-tense form meaning resembles or looks like.

Its dictionary form is أشبهَ.
So:

• أشبهَ = to resemble
• يُشْبِهُ = he/it resembles

Because هذا is masculine singular, the verb appears in the he/it form: يشبه.

Because يشبه already contains the idea of resembling. In English, you often say looks like or is like, but in Arabic this verb can directly take an object:

• هذا يشبه صديقي = This resembles my friend

So you do not need an extra word meaning like here.

Yes. صديقي is the direct object of يشبه.

The sentence structure is basically:

• هذا = this
• يشبه = resembles
• صديقي = my friend

So literally: This resembles my friend.

The ending ـي on صديق means my.

So:

• صديق = friend
• صديقي = my friend

This ـي is a attached pronoun meaning my. It is one of the most common possession endings in Arabic.

Because a possessed noun is already definite in Arabic.

So صديقي already means my friend, which is definite. You do not normally add ال to it here.

Compare:

• صديق = a friend / friend
• صديقي = my friend

Good question. Grammatically, صديقي is the object, so it is accusative. But when a noun is followed by the my ending ـي, the case ending is usually not visible in normal writing.

So even though it is functioning as the object, the written form still appears as صديقي.

In other words:

• its grammatical role is clear from the sentence
• its case ending is not obvious on the surface because of the attached ـي

Starting with هذا is very natural when you are pointing something out.

It is like saying:

• This — it resembles my friend.

So the sentence begins with the thing being pointed at, and then gives information about it. This is a very common Arabic pattern with demonstratives such as هذا and هذه.

It can refer to a person too.

Depending on context, هذا can mean:

• this thing
• this man
• this person (if masculine)

So هذا يشبه صديقي could be said about a man, a boy, or even an object, depending on what you are pointing at.

A careful pronunciation is:

hādhā yushbihu ṣadīqī

A few helpful notes:

• ذ in هذا sounds like the th in this
• ص in صديقي is a heavy or emphatic s
• the long ī at the end of صديقي should be held a little longer

In pause, learners may also hear the last short vowel of يشبه dropped, so it can sound closer to yushbih.

You would say:

هذه تشبه صديقي

Changes:

• هذا becomes هذه
• يشبه becomes تشبه

That is because the subject is now feminine singular, so the verb changes to match it.

Yes. Another common pattern is to use مشابه لـ:

هذا مشابهٌ لصديقي

This also means something like This is similar to my friend.

The difference is:

• يشبه is a verb: resembles
• مشابه is more like similar

Your original sentence uses the verb pattern, which is very natural and common.