Każdy pracownik ma swoje obowiązki, ale dobrzy współpracownicy pomagają sobie nawzajem.

Because każdy means each / every and in Polish it is used with a singular noun.

So Polish says:

• Każdy pracownik ma... = Every employee has...

Even though the meaning is about all employees in general, the grammar is singular. That is also why the verb is singular: ma, not mają.

If you wanted to say all employees, you would use a plural phrase such as wszyscy pracownicy mają...

Because swoje agrees with obowiązki, not with pracownik.

In Polish, possessive words like swój change to match the thing being possessed:

• swój obowiązek = one duty
• swoje obowiązki = duties

Here, obowiązki is plural, so swoje is also plural.

So even though pracownik is singular, swoje is plural because the employee has multiple duties.

Polish normally uses swój when the possessor is the same as the subject of the clause.

So:

• Każdy pracownik ma swoje obowiązki = each employee has their own duties

This is the natural Polish way to say that someone has their own something.

Using jego or jej would usually sound like you mean someone else’s duties, or it could create ambiguity.

A useful rule:

• if the subject owns it, use swój
• if someone else owns it, use jego / jej / ich

It is in the accusative plural because it is the direct object of ma from mieć.

The verb mieć takes the accusative:

• mam książkę
• mam obowiązki

With obowiązek, the plural form obowiązki looks the same in the nominative and accusative, so you do not see a difference in the ending here.

Because współpracownicy refers to people, and in Polish male-person or mixed-person groups use the masculine personal plural form.

That affects both the noun and the adjective:

• dobry współpracownik = a good coworker
• dobrzy współpracownicy = good coworkers

The adjective dobry changes to dobrzy for masculine personal plural.

By contrast, dobre is used for non-masculine-personal plurals, not for a group of male or mixed-gender people.

That is the normal nominative plural pattern for many masculine personal nouns ending in -nik or -ownik.

For example:

• pracownik → pracownicy
• robotnik → robotnicy
• współpracownik → współpracownicy

So this is not an unusual form once you get used to masculine personal plurals in Polish.

Because the verb pomagać takes the dative, not the accusative.

You can think of it as answering the question:

• pomagać komu? czemu? = to help to whom?

So the correct reflexive pronoun is sobie (dative), not siebie.

• pomagają sobie = they help themselves / each other

With a plural subject, this often has a reciprocal meaning.

Nawzajem means mutually, each other, or one another.

So:

• pomagają sobie can already mean they help each other
• pomagają sobie nawzajem makes that mutual meaning extra clear and explicit

It is a very natural phrase in Polish.

So the second clause is not just they help but specifically they help one another.

Because each verb agrees with its subject:

• Każdy pracownik is grammatically singular → ma
• Dobrzy współpracownicy is plural → pomagają

This is a very important point in Polish: even when każdy means something general like every, it still takes singular agreement.

Yes. Polish word order is fairly flexible because endings carry a lot of grammatical information.

The original sentence is a neutral, natural order:

• Każdy pracownik ma swoje obowiązki, ale dobrzy współpracownicy pomagają sobie nawzajem.

You could change the order for emphasis, for example:

• Ale dobrzy współpracownicy pomagają sobie nawzajem.
• Swoje obowiązki ma każdy pracownik...
  This sounds more emphatic or stylistically marked.

So the original version is probably the best one for a learner to use first.

They are related but not the same:

• pracownik = employee, worker
• współpracownik = coworker, colleague

So in this sentence:

• każdy pracownik talks about each employee as an individual worker
• dobrzy współpracownicy talks about coworkers in relation to one another

That is why both words appear in the same sentence without being redundant.