Ovo je naša dužnost.

Word by word:

• Ovo = this
• je = is
• naša = our
• dužnost = duty

A more grammatical breakdown:

• ovo is a demonstrative pronoun
• je is the 3rd person singular present of biti (to be)
• naša is a possessive adjective/pronoun
• dužnost is a noun

So the structure is basically:

This is our duty.

Because ovo is the neuter singular form used when this stands on its own, without directly modifying a noun.

Compare:

• Ovo je naša dužnost. = This is our duty.
• Ova dužnost je važna. = This duty is important.

In the first sentence, ovo is not attached to a noun right after it, so Croatian usually uses the neutral standalone form ovo.

Very roughly:

• ovaj = this (masculine)
• ova = this (feminine)
• ovo = this (neuter / standalone this)

Because it agrees with dužnost, which is a feminine singular noun.

In Croatian, words like our change form to match the noun’s:

• gender
• number
• case

So:

• naš = masculine singular
• naša = feminine singular
• naše = neuter singular

Since dužnost is feminine, you need naša:

• naša dužnost = our duty

It is in the nominative singular.

This is because the sentence is an equational sentence with to be:

• Ovo = subject-like element
• je = is
• naša dužnost = predicate noun phrase

In Croatian, after biti in this kind of sentence, the noun phrase is normally in the nominative:

• Ovo je problem.
• To je istina.
• Ovo je naša dužnost.

So dužnost is nominative singular, and naša matches it.

You usually learn noun gender together with the noun, but there are also patterns.

Dužnost is one of many feminine nouns ending in -ost:

• radost = joy
• mudrost = wisdom
• dužnost = duty

These are typically feminine.

You can also see it from agreement:

• naša dužnost
  not
• naš dužnost

So the sentence itself confirms the noun is feminine.

Because Croatian does not have articles like English a/an/the.

So Croatian often expresses definiteness through:

• context
• word order
• demonstratives like ovaj / ta / onaj
• possessives like moj, naš, njihov

In naša dužnost, the possessive naša already makes the phrase specific enough: our duty.

That is why Croatian can simply say:

• Ovo je naša dužnost.

with no separate word for the.

The normal, neutral order is:

• Ovo je naša dužnost.

But Croatian word order is more flexible than English, and changing it can change the emphasis.

For example:

• Naša dužnost je ovo. = Our duty is this.
  This sounds more contrastive or emphatic.

• Je li ovo naša dužnost? = Is this our duty?

So yes, the words can move, but the neutral version for a plain statement is the original one.

Yes, very often.

Both ovo and to can appear in sentences like this, but they are not exactly the same.

• ovo = this, something close, immediate, or being pointed out now
• to = often that, but also commonly used in general identification statements

Compare:

• Ovo je naša dužnost. = This is our duty.
• To je naša dužnost. = That/This is our duty.

In real usage, to je is extremely common, sometimes even where English would use this is.

Because Croatian does not need a dummy pronoun like English sometimes does.

In this sentence, ovo already serves as the thing being identified:

• Ovo je naša dužnost. = literally This is our duty.

English sometimes uses pronouns differently, but Croatian can simply use a demonstrative like ovo or to.

So there is no missing word here; ovo is doing that job.

A simple English-friendly approximation is:

• DOOZH-nost

Useful sound notes:

• du sounds like doo
• ž sounds like the s in measure or pleasure
• nost is pronounced clearly, with a short o

So the whole sentence can be approximated as:

• OH-vo yeh NAH-sha DOOZH-nost

A few key letter values:

• j = English y
• š = sh
• ž = the sound in measure

The most standard way is:

• Je li ovo naša dužnost? = Is this our duty?

You may also hear:

• Je ovo naša dužnost?

And in speech, intonation alone can sometimes do it:

• Ovo je naša dužnost?

But for learners, Je li ... ? is the safest standard pattern to use.

It would become:

• Ovo su naše dužnosti. = These are our duties.

What changed:

• je → su (is → are)
• naša → naše to agree with the plural noun
• dužnost → dužnosti (plural)

So this sentence is a good example of agreement across the whole noun phrase.