Zaista znam odgovor.

Zaista means really / truly / indeed. In this sentence, it adds emphasis: I really do know the answer.

It is correct and natural, but in very casual speech many Croatians might also say:

• Stvarno znam odgovor.
• Doista znam odgovor.

Very roughly:

• zaista = really, indeed
• doista = indeed, truly; often a bit more formal or careful
• stvarno = really; very common in everyday speech

So Zaista znam odgovor. sounds fine, just slightly more deliberate than the most casual option.

Yes. You can simply say:

• Znam odgovor.

That means I know the answer.

Adding zaista gives extra emphasis, like:

• I really know the answer
• I truly know the answer

So the sentence without zaista is more neutral.

Because the verb znati in this meaning takes a direct object, and the direct object normally goes in the accusative case.

Here:

• znam = I know
• odgovor = answer

The noun odgovor is masculine inanimate. For many masculine inanimate nouns in Croatian, the accusative singular looks exactly the same as the nominative singular.

So:

• nominative: odgovor
• accusative: odgovor

That is why you see znam odgovor.

By contrast, with a masculine animate noun, nominative and accusative would differ more clearly.

You know from the role in the sentence, not just the form.

In Zaista znam odgovor.:

• (ja) is the understood subject = I
• znam is the verb
• odgovor is what is known, so it is the direct object

Since direct objects after znati are usually accusative, odgovor is accusative here, even though its form is identical to nominative.

This is very common in Croatian with masculine inanimate nouns.

Because Croatian often omits subject pronouns when they are already clear from the verb form.

• znam already means I know

So ja is not necessary.

You could say:

• Ja zaista znam odgovor.

But adding ja usually gives extra emphasis, something like:

• I really do know the answer
• I know the answer, honestly

So the version without ja is the normal neutral one.

Yes. Croatian word order is fairly flexible, and changing it often changes the emphasis, not the basic meaning.

Possible versions include:

• Zaista znam odgovor. = neutral emphasis on really
• Znam odgovor zaista. = possible, but less natural in many contexts
• Odgovor zaista znam. = emphasizes the answer
• Ja zaista znam odgovor. = emphasizes I

The most natural basic version here is the one you were given: Zaista znam odgovor.

Znam odgovor is correct for I know the answer.

Be careful not to confuse:

• znati = to know
• odgovor = answer (a noun)
• odgovoriti = to answer (a verb)

So:

• Znam odgovor. = I know the answer.
• Mogu odgovoriti. = I can answer.
• Odgovorit ću. = I will answer.

English uses answer as both a noun and a verb, but Croatian uses different forms.

Croatian uses different verbs for different kinds of know.

Here, znati is correct because it means knowing a fact, piece of information, or answer.

• znam odgovor = I know the answer
• znam istinu = I know the truth

But for being familiar with a person or place, Croatian often uses poznavati or poznavati/poznavati in practice through forms like poznajem:

• Poznajem Marka. = I know Marko.
• Poznajem taj grad. = I know that city.

So znam odgovor is correct because this is knowledge of information, not familiarity with a person or place.

A simple learner-friendly pronunciation is:

• ZAI-sta znam OD-go-vor

A few helpful points:

• z sounds like the z in zoo
• aj sounds roughly like eye
• st is pronounced clearly in zaista
• zn at the start of znam is pronounced with both sounds; Croatian allows that consonant cluster
• r in odgovor is a rolled or tapped r

Very approximate English-style guide:

• ZAI-sta znam OD-go-vor

Because Croatian has no articles like English a/an/the.

So odgovor can mean:

• an answer
• the answer

The exact meaning depends on context.

In this sentence, the intended meaning is the answer, but Croatian does not need a separate word for the.

In theory, yes, because odgovor without an article can be interpreted from context.

But in a normal situation, Znam odgovor is usually understood as I know the answer, especially if there is a specific question being discussed.

If you wanted to make it more indefinite in context, Croatian would usually rely on the situation or add other words rather than using an article, since it has none.

Not necessarily stronger, but it can sound a bit more deliberate, sincere, or insistent depending on context.

For example:

• Zaista znam odgovor. can sound like
  I really do know the answer.

It may be used when someone doubts you, or when you want to reassure them that you truly know it.

So the force depends a lot on tone and context, just as really can in English.

Yes, very naturally.

For example, if someone says or implies that you do not know, you could reply:

• Zaista znam odgovor.

That can mean something like:

• I really do know the answer.
• Honestly, I know the answer.

If you want even stronger contrast, you could say:

• Ja zaista znam odgovor.
• Zaista znam odgovor, vjeruj mi. = I really know the answer, believe me.