Behandlingen gjør hundens pels myk.

Because behandling is the noun treatment, and -en is the definite singular ending for many common-gender nouns in Bokmål.

So:

• en behandling = a treatment
• behandlingen = the treatment

Norwegian usually puts definiteness at the end of the noun instead of using a separate word like the.

Here gjør means makes.

It is the present tense of gjøre, which often means do, but in this kind of sentence it means make or cause to become.

The pattern is:

gjøre + object + adjective

So:

• gjør hundens pels myk = makes the dog's fur soft

A very common parallel is:

• gjøre huden myk = make the skin soft

Hundens is the genitive form, similar to English apostrophe-s.

It comes from:

• hunden = the dog
• hundens = the dog's

So Norwegian adds -s to the noun phrase to show possession.

Compare:

• hunden = the dog
• hundens pels = the dog's fur

This is one of the main ways to express possession in Norwegian.

Because when a noun is possessed by a genitive phrase like hundens, the possessed noun usually stays in its basic form.

So Norwegian says:

• hundens pels = the dog's fur

not:

• hundens pelsen

The whole phrase is already definite because of the possessor. English does something similar: we say the dog's fur, not the dog's the fur.

Because myk agrees with pels, and pels is a singular common-gender noun.

In this sentence, myk is a result adjective after gjør, and it agrees in gender and number like this:

• common gender singular: myk
• neuter singular: mykt
• plural: myke

So:

• hundens pels → myk
• håret → mykt
• potene → myke

Also, even though hundens pels is definite in meaning, predicative/result adjectives like this do not use the special definite adjective form.

Compare:

• Pelsen er myk
• Behandlingen gjør pelsen myk

not myke.

Because pels usually means fur or coat, especially for animals.

So for a dog, pels is the natural word.

Very roughly:

• hår = hair
• pels = fur / coat

You can think of hundens pels as the dog's fur or the dog's coat.

Yes. Pelsen til hunden is also correct and means the same thing.

So these are both possible:

• hundens pels
• pelsen til hunden

The -s genitive (hundens pels) is shorter and often feels more compact.
The til construction is also common, especially when the possessor is longer or more complicated.

A learner should understand both.

The sentence follows a very common Norwegian pattern:

subject + verb + object + result adjective

So here:

• Behandlingen = subject
• gjør = finite verb
• hundens pels = object
• myk = result adjective

That gives:

Behandlingen gjør hundens pels myk.

This is normal Norwegian main-clause word order. The finite verb comes early in the sentence, in second position overall.

Yes. Behandling can mean treatment, but the exact nuance depends on context.

For example, it could refer to:

• a grooming treatment
• a medical treatment
• a conditioning treatment
• some kind of care process

In this sentence, because it affects hundens pels, it most naturally sounds like some kind of coat, fur, or grooming treatment.