Hendes onkel arbejder i havnen, og han siger, at der er roligere om morgenen.

Hendes means her.

In Danish, a possessive usually replaces an article, so you say hendes onkel = her uncle, not en hendes onkel or den hendes onkel.

It is not sin onkel because sin/sit/sine is reflexive. Those forms are used when the possessor is the same as the subject of the clause. Here, hendes refers to some woman or girl, while the subject is onkel, so Danish uses hendes, not sin.

Danish verbs do not change by person the way English verbs do.

So:

• jeg arbejder = I work
• du arbejder = you work
• han arbejder = he works
• vi arbejder = we work

The -er ending here is the present tense form, and it stays the same for all persons.

I usually means in or at for many places and areas.

So arbejder i havnen means works in/at the harbor.

Also, havnen is the definite form of havn:

• en havn = a harbor
• havnen = the harbor

Danish often puts the definite article at the end of the noun instead of using a separate word like the.

Sometimes yes, depending on dialect, context, and nuance. But i havnen is the most straightforward choice here.

A simple way to think about it is:

• i havnen = in the harbor area / at the harbor
• på is more often used for surfaces, islands, and some institutional or set location expressions

So for a learner, i havnen is the safest form to use in this sentence.

Yes, it could.

Both of these are possible:

• Hendes onkel arbejder i havnen og siger, at ...
• Hendes onkel arbejder i havnen, og han siger, at ...

Including han makes the second clause more explicit and clearly separates the two actions:

• he works in the harbor
• he says that it is calmer in the morning

So the version with og han siger sounds a little fuller and clearer, especially in normal prose.

Here at means that.

It introduces a subordinate clause:

• han siger = he says
• at der er roligere om morgenen = that it is calmer in the morning

In everyday English, that is often omitted: he says it is calmer in the morning. Danish can also sometimes omit at in speech, but using it is very common and clear.

Der er is a very common Danish structure used to express that something exists or that a condition holds somewhere/somehow. It often corresponds to English there is/there are, but in translation it may sound more natural as it is.

So:

• der er roligere om morgenen literally looks like there is calmer in the morning
• natural English: it’s calmer in the morning

Danish and English do not always package this kind of idea the same way.

Not really in a literal location sense.

In der er, der is often a grammatical placeholder, sometimes called a dummy subject. It helps build the sentence, but it does not strongly mean a physical there.

So in this sentence, der is part of the structure der er rather than a word pointing to a place.

Roligere is the comparative form of rolig.

• rolig = calm / quiet
• roligere = calmer / quieter

Many Danish adjectives form the comparative with -ere, just as many English adjectives use -er.

So the sentence is saying that mornings are calmer/quieter than some other time.

Because Danish, like English, can use a comparative without stating both sides explicitly when the comparison is obvious.

So der er roligere om morgenen naturally means something like:

• it is calmer in the morning than later in the day
• it is quieter in the morning than at other times

The second half of the comparison is understood from context.

No. Here om is part of a time expression.

Om morgenen means in the morning.

This is a very common Danish pattern for general or habitual times:

• om morgenen = in the morning
• om aftenen = in the evening
• om natten = at night

So the sentence means that this is generally true in the mornings, not just on one specific morning.

In this fixed time expression, Danish normally uses the definite form:

• morgen = morning
• morgenen = the morning

So om morgenen literally looks like in the morning, which matches natural English quite well.

Be careful not to confuse it with i morgen, which means tomorrow.

Yes. After at, you are in a subordinate clause, and Danish does not use normal main-clause verb-second word order there.

In this sentence, the clause is:

• at der er roligere om morgenen

That word order is normal for a subordinate clause.

You can see the difference more clearly if an adverb is added:

• main clause: Der er ikke roligere om morgenen.
• subordinate clause: Han siger, at der ikke er roligere om morgenen.

So after at, words like ikke usually come before the finite verb in a way that differs from main clauses.

The commas help separate the clauses:

• Hendes onkel arbejder i havnen
• og han siger
• at der er roligere om morgenen

Many Danish writers use a comma before at. In modern Danish, this can depend on comma style, so you may also see han siger at ... without that comma.

The comma before og helps show that two full clauses are being linked.