Policajac obavlja svoju dužnost.

Policajac literally means a male police officer / policeman. In modern English, police officer is often the most natural translation.

A few useful notes:

• policajac = male officer
• policajka = female officer
• Croatian often uses the masculine form in dictionary entries and general examples.

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

So Policajac obavlja svoju dužnost can mean:

• The police officer is carrying out his duty
• A police officer carries out his duty

Which one sounds best depends on context. Croatian leaves that to the situation rather than marking it with an article.

Obavlja is the 3rd person singular present tense form of obavljati.

So:

• ja obavljam = I carry out
• ti obavljaš = you carry out
• on/ona obavlja = he/she carries out

Because the subject is policajac (he), Croatian uses obavlja.

It can mean any of those, depending on context.

Because obavljati is imperfective, the present tense can describe:

• something happening right now: is carrying out
• something done regularly / habitually: carries out
• a more general action: does / performs

So this sentence could be understood as:

• The police officer is carrying out his duty
• The police officer performs his duty

English chooses between simple present and progressive more strictly than Croatian does.

Croatian uses svoj when the possessor is the same as the subject of the sentence.

Here, the subject is policajac, so:

• svoju dužnost = his own duty

If you said njegovu dužnost, it would usually mean the duty belonging to some other male person, not the subject himself.

This is a very important Croatian pattern:

• Ivan voli svoju obitelj. = Ivan loves his own family.
• Ivan voli njegovu obitelj. = Ivan loves his family, meaning someone else’s family.

Svoju is the accusative singular feminine form of svoj.

It has that form because it agrees with dužnost, which is:

• feminine
• singular
• here in the accusative, because it is the direct object of the verb

So:

• svoja dužnost would be nominative
• svoju dužnost is accusative

The adjective has to match the noun in gender, number, and case.

Dužnost is in the accusative singular here because it is the direct object of obavlja.

Its dictionary form is dužnost, which is nominative singular. In this noun type, the accusative singular has the same form as the nominative singular, so it looks unchanged.

So:

• nominative: dužnost
• accusative: dužnost

That is normal for many feminine nouns ending in -ost.

Yes. Croatian word order is more flexible than English word order because case endings show grammatical relationships.

The neutral order here is:

• Policajac obavlja svoju dužnost.

But you could also hear:

• Svoju dužnost obavlja policajac.
• Policajac svoju dužnost obavlja.

These alternatives change the focus or emphasis, not the basic meaning.

For example:

• Svoju dužnost obavlja policajac can sound more like It is his duty that the police officer is carrying out or can emphasize svoju dužnost.

Yes, you can, but the nuance changes a little.

• Policajac obavlja svoju dužnost = the officer is carrying out his own duty
• Policajac obavlja dužnost = the officer is carrying out duty / his duty, with less emphasis on possession

Including svoju makes the relationship clearer and sounds more explicit. Without it, the sentence is still understandable, but slightly less specific.

Obavljati is imperfective.

That matters because imperfective verbs are used for:

• ongoing actions
• repeated actions
• general processes

Its perfective partner is usually obaviti, which means to complete / finish carrying out something.

Compare:

• Policajac obavlja svoju dužnost. = The police officer is carrying out his duty.
• Policajac je obavio svoju dužnost. = The police officer carried out / completed his duty.

So in your sentence, the focus is on the action as ongoing or general, not on its completion.