Ova knjiga je tvoja.

Because knjiga is a feminine singular noun, and ova has to agree with it.

The demonstrative ovaj meaning this changes form by gender:

• ovaj = masculine
• ova = feminine
• ovo = neuter

So:

• ova knjiga = this book
• ovaj sto = this table
• ovo pismo = this letter

Agreement is very important in Serbian.

For the same reason: tvoja must agree with knjiga.

The word tvoj means your, but it changes form depending on the noun it describes:

• tvoj = masculine
• tvoja = feminine
• tvoje = neuter

So:

• tvoj brat = your brother
• tvoja knjiga = your book
• tvoje dete = your child

In Ova knjiga je tvoja, the understood noun is still knjiga, so the feminine form tvoja is used.

Je is the 3rd person singular present tense of biti = to be.

So the sentence structure is:

• Ova knjiga = this book
• je = is
• tvoja = yours / your one

So je is simply the word is.

Because je is a clitic in Serbian. Clitics are short unstressed words that usually appear in the second position in a sentence or clause.

In Ova knjiga je tvoja, the first unit is Ova knjiga, and then the clitic je comes after it.

This is very normal Serbian word order.

You will often see similar patterns:

• Marko je ovde. = Marko is here.
• Moja sestra je doktor. = My sister is a doctor.

Yes, Serbian word order is fairly flexible, but changing it usually changes the emphasis.

The most neutral version is:

• Ova knjiga je tvoja.

Other possible versions might emphasize different things, for example:

• Tvoja je ova knjiga. = It’s yours, this book.
• Je li ova knjiga tvoja? = Is this book yours?

So the basic meaning can stay the same, but the focus or tone may shift.

It behaves like a possessive adjective, because it agrees with the noun in gender, number, and case.

But in this sentence it is used predicatively, meaning it comes after je and works a bit like English yours.

Compare:

• Ovo je tvoja knjiga. = This is your book.
  Here tvoja directly describes knjiga.

• Ova knjiga je tvoja. = This book is yours.
  Here tvoja is part of the predicate after je.

So in English the second one looks like a pronoun (yours), but in Serbian the form still matches the noun like an adjective.

Because it is the subject of the sentence, so it is in the nominative singular:

• knjiga = nominative singular

If the noun had a different role, it would change form. For example:

• Vidim ovu knjigu. = I see this book.
  Here knjigu is accusative.

In Ova knjiga je tvoja, knjiga is the thing being talked about as the subject, so nominative is required.

Yes. That means The book is yours.

Adding ova makes it specifically this book. Without ova, the sentence is less specific and depends more on context.

Compare:

• Knjiga je tvoja. = The book is yours.
• Ova knjiga je tvoja. = This book is yours.

These are different demonstratives:

• ova = this
• ta = that
• ona = that over there / that one

With knjiga:

• ova knjiga = this book
• ta knjiga = that book
• ona knjiga = that book over there

In practice, exact usage can depend on context, but this is a good basic distinction.

A very common way is:

• Da li je ova knjiga tvoja? = Is this book yours?

You can also say:

• Je li ova knjiga tvoja?

Both are used. The da li version is often easier for learners because it is very clear and straightforward.

Normally, no. In a standard sentence like this, je should be present.

So:

• Ova knjiga je tvoja. = correct

Leaving it out would sound incomplete in normal Serbian:

• Ova knjiga tvoja. = not standard as a full sentence

Serbian usually requires the present tense of to be in this kind of sentence.