Urmakeren kontrollerer opptrekkskronen og spennen.

Because -en is the usual definite singular ending for many masculine nouns in Norwegian.

• urmaker = watchmaker

• urmakeren = the watchmaker

• opptrekkskrone = winding crown / watch crown

• opptrekkskronen = the winding crown

• spenne = buckle / clasp
• spennen = the buckle / clasp

Unlike English, Norwegian usually puts the definite article at the end of the noun instead of using a separate word like the.

In Norwegian, definiteness is often built into the noun itself.

So English:

• the watchmaker

becomes Norwegian:

• urmakeren

This is very normal in Norwegian. A separate article such as den is usually only added in certain patterns, for example with adjectives:

• den gamle urmakeren = the old watchmaker

But with a plain noun by itself, urmakeren is enough.

Kontrollerer is the present tense of å kontrollere = to check / inspect / examine.

Examples:

• jeg kontrollerer = I check
• du kontrollerer = you check
• han kontrollerer = he checks

A key difference from English: the verb form does not change depending on the subject. Norwegian uses the same present-tense form for all persons.

It can mean both, depending on context.

Norwegian present tense often covers both:

• checks
• is checking

So this sentence could mean:

• The watchmaker checks the winding crown and the clasp or
• The watchmaker is checking the winding crown and the clasp

Context tells you which one is meant.

That -s- is a linking element used in compounds. It is very common in Norwegian.

Here the word is built like this:

• opptrekk = winding
• krone = crown
• opptrekkskrone = winding crown
• opptrekkskronen = the winding crown

That -s- does not mean possession here in the English sense. It is just part of how many compound nouns are formed.

Yes. Norwegian very often writes compound nouns as one word, where English might use two words or even a hyphenated expression.

So:

• opptrekkskrone = one word
• not opptrekks krone

This is an important habit to learn, because splitting compounds can look unnatural or even change the meaning.

Spenne can mean buckle, clasp, or a similar fastening device, depending on context.

In a watch-related sentence, spennen most likely means:

• the buckle on a strap or
• the clasp on a bracelet

So the exact English translation depends on what kind of watch band is being discussed.

The sentence follows the normal Norwegian main-clause pattern:

• Urmakeren = subject
• kontrollerer = verb
• opptrekkskronen og spennen = object

So it is basically:

Subject + Verb + Object

This is very similar to ordinary English word order:

• The watchmaker checks the winding crown and the clasp.

For the same reason as with urmakeren: the definiteness is built into the noun endings.

So:

• opptrekkskronen already means the winding crown
• spennen already means the buckle/clasp

You do not need a separate the in front.

No. Og simply means and and joins words or phrases together.

Here it joins two definite singular nouns:

• opptrekkskronen
• spennen

So the structure is just:

• the winding crown and the clasp

Nothing special happens to the nouns because of og.

It would be:

En urmaker kontrollerer en opptrekkskrone og en spenne.

That means:

A watchmaker checks a winding crown and a buckle/clasp.

Notice the changes:

• urmakeren → en urmaker
• opptrekkskronen → en opptrekkskrone
• spennen → en spenne

So the ending -en disappears, and an indefinite article like en is used instead.

A rough guide is:

• urmakeren ≈ OOR-mah-keh-ren

Things to notice:

• u in ur is not like the English u in up. It is a more rounded vowel.
• The r is pronounced more clearly than in many English accents.
• The stress is mainly on the first part: URmakeren.

Even if your pronunciation is not perfect, getting the rhythm right will help a lot.

It sounds natural, but the vocabulary is somewhat technical because it is about watch parts.

• Urmakeren kontrollerer ... is straightforward and normal Norwegian.
• opptrekkskronen is specialized vocabulary connected to watches.
• spennen is less technical, but its exact meaning depends on the watch context.

So the grammar is everyday Norwegian, while part of the vocabulary is domain-specific.