Çantadaki anahtar benim.

Çantadaki can be broken down like this:

• çanta = bag
• -da = in / at / on
  → çantada = in the bag
• -ki = a suffix that turns that location phrase into something like the one in... or the ... that is in...

So:

• çantada = in the bag
• çantadaki = the one in the bag / the thing that is in the bag

In this sentence, çantadaki describes anahtar, so çantadaki anahtar means the key in the bag.

Here, -ki turns a phrase into an adjective-like modifier.

Without -ki:

• çantada anahtar would just suggest something like a key is in the bag in a looser sense.

With -ki:

• çantadaki anahtar = the key that is in the bag

So -ki is very useful when Turkish wants to say things like:

• masadaki kitap = the book on the table
• odadaki insan = the person in the room
• çantadaki anahtar = the key in the bag

It works a bit like English that is in/on/at...

Yes, benim often means my before a noun:

• benim anahtarım = my key

But benim can also stand on its own and mean mine in sentences like this:

• Bu kitap benim. = This book is mine.
• Çantadaki anahtar benim. = The key in the bag is mine.

So here benim is not directly modifying a noun. It is acting like mine.

Good question. Benimki means mine / the one that is mine, but it is used a little differently.

• Bu benim. = This is mine.
• Bu benimki. = This is mine / this one is the one that belongs to me.

In many simple ownership sentences, Turkish normally uses benim:

• Araba benim. = The car is mine.
• Anahtar benim. = The key is mine.

Benimki is more likely when you are contrasting one item with another:

• Seninki kırmızı, benimki mavi. = Yours is red, mine is blue.
• Masadaki seninki, çantadaki benimki. = The one on the table is yours, the one in the bag is mine.

So in your sentence, benim is the most natural choice.

In the present tense, Turkish often has no separate word for is / am / are in simple statements.

So:

• Anahtar benim. literally looks like key mine
• but it means The key is mine

This is completely normal in Turkish.

If you want past tense, then a visible form appears:

• Anahtar benimdi. = The key was mine.

So the present-tense copula is often just understood.

Turkish often puts the topic or subject first and the predicate last.

So:

• Çantadaki anahtar = the key in the bag
• benim = mine

Together:

• Çantadaki anahtar benim. = The key in the bag is mine.

This is a very natural Turkish order.

You could change the order for emphasis in some contexts, but this version is the basic, neutral one.

Turkish does not have articles like English the and a/an.

Whether something is understood as the key or a key depends on context.

Here, çantadaki anahtar is naturally understood as the key in the bag, because the phrase is specific. You are talking about a particular key, namely the one located in the bag.

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

Because the possession here is expressed by the separate predicate benim, not by attaching a possessive suffix to anahtar.

Compare:

• anahtarım = my key
• Anahtar benim. = The key is mine.

These are two different structures:

1. Possessive noun phrase

   • benim anahtarım = my key

2. Sentence saying ownership

   • Anahtar benim. = The key is mine.

So in Çantadaki anahtar benim, the noun anahtar stays plain, and ownership is shown at the end with benim.

Not in good English, but that helps show the structure.

A very rough word-for-word breakdown is:

• çantadaki = in-the-bag / the one in the bag
• anahtar = key
• benim = mine / belonging to me

So the natural English translation is:

• The key in the bag is mine.

Trying to map every Turkish word directly onto English grammar can be misleading, especially with benim and with the missing is.

Yes. Turkish often lets -ki phrases stand on their own when the noun is understood.

For example:

• Çantadaki benim. = The one in the bag is mine.

This works when the listener already knows what kind of thing you mean.

But in your sentence, anahtar is included to make it explicit:

• Çantadaki anahtar benim. = The key in the bag is mine.

Yes, it is possible.

• Çantadaki anahtar benim.
• Çantadaki anahtar benimdir.

Both mean The key in the bag is mine.

The form -dir can sound more formal, more definite, or more emphatic depending on context. In everyday speech, people usually just say:

• Çantadaki anahtar benim.

So the version without -dir is the most common conversational form.

It is in the locative case:

• çanta = bag
• çantada = in the bag

The locative ending is usually one of these:

• -da
• -de
• -ta
• -te

Which one appears depends on vowel harmony and consonant voicing.

Here:

• çanta ends in a voiceless consonant t
• so the locative becomes -ta
• çanta + da/de/ta/te → çantada is the standard spelling and pronunciation pattern here because the base already ends with ta sound sequence? More practically, the full form is learned as çantada.

Then -ki is added:

• çantada + ki → çantadaki

Yes, very much so.

English says:

• the key that is in the bag

Turkish often expresses that idea more compactly with -ki:

• çantadaki anahtar

So this phrase functions a lot like an English relative clause, but the Turkish structure is shorter and built with a suffix.

That is why learners often think of -ki as meaning something like:

• the one in...
• that is in...

Both are useful ways to understand it.