Masadaki kitap benim.

Masadaki is built in two steps:

• masa = table
• masa-da = on the table / at the table / in the table's location
• masa-da-ki = the one that is on the table

So masadaki kitap literally means something like the book that is on the table.

In natural English, that becomes the book on the table.

Here, -ki turns a phrase like masada into something that can describe a noun.

So:

• masada = on the table
• masadaki kitap = the book on the table

You can think of -ki as creating a short relative expression, similar to that is on in English.

More examples:

• evdeki çocuk = the child in the house
• çantadaki anahtar = the key in the bag
• raftaki kitap = the book on the shelf

Because masada kitap is not the same kind of structure.

• masada kitap is more like a clause or statement about a book being on the table
• masadaki kitap is a noun phrase: the book on the table

So if you want to identify which book, Turkish uses -ki:

• masadaki kitap = the book on the table

Without -ki, you do not get that same modifier + noun meaning.

Because in Turkish, words that describe a noun normally come before the noun.

So:

• masadaki kitap = the book on the table
• literally: on-the-table book

This is very normal Turkish word order. The describing part comes first, and the noun it describes comes after.

Turkish often leaves out the verb to be in the present tense, especially in third person singular.

So:

• Masadaki kitap benim = The book on the table is mine.

There is no separate word for is here, but it is understood.

A more formal or emphatic version can use -dir:

• Masadaki kitap benimdir.

That still means the same thing, but sounds more formal, definite, or emphatic.

Benim is the genitive form of ben (I), and it often means my / of me.

For example:

• benim kitabım = my book

But when benim stands as the predicate in a sentence like this, it means mine:

• Bu kitap benim. = This book is mine.
• Masadaki kitap benim. = The book on the table is mine.

So here benim is not translating as my but as mine.

Because benim is the normal way to say is mine in this kind of sentence.

• Bu kitap benim. = This book is mine.

Benimki means mine / my one as a standalone noun phrase, often when contrasting it with someone else's:

• Seninki kırmızı, benimki mavi. = Yours is red, mine is blue.

So:

• Masadaki kitap benim = the normal basic sentence
• benimki is more like my one / the one belonging to me

A learner should first get comfortable with X benim = X is mine.

Because kitap is not being said as my book inside the noun phrase.

The structure is:

• Masadaki kitap = the book on the table
• benim = is mine

So the possession is expressed in the predicate, not on kitap itself.

Compare:

• benim kitabım = my book
• Masadaki kitap benim. = The book on the table is mine.

These are different structures.

In Turkish, nouns do not have articles like a or the.

Whether kitap is understood as a book or the book depends on context.

In this sentence, masadaki makes the noun specific, so in English it is naturally translated as:

• the book on the table

So even though there is no separate word for the, the meaning is definite.

In this use, -ki stays as -ki. It does not change like many other Turkish suffixes do.

What changes is the locative part before it:

• masa-da-ki
• ev-de-ki
• raf-ta-ki
• bahçe-de-ki

So the -da / -de / -ta / -te part changes as normal, but -ki remains ki.

Yes. That is correct.

• Masadaki kitap benim.
• Masadaki kitap benimdir.

Both mean the same basic thing.

The version with -dir is usually:

• more formal
• more emphatic
• sometimes more assertive

In everyday speech, Masadaki kitap benim is more common.