Han mister evnen.

Evne is the indefinite singular form, roughly an ability.
Evnen is the definite singular form, roughly the ability.

In Norwegian, the definite article is usually attached to the end of the noun, so -en is doing the job that English the does.

Mister is the present tense of å miste.

Useful forms:

• å miste — infinitive
• mister — present
• mistet / mista — past
• har mistet — present perfect

Depending on context, English might translate this as loses or is losing.

No. Here mister means loses.

So Han mister evnen is about losing an ability, not missing one.

For miss someone, Norwegian usually uses savner.

Because han is the subject form, like English he. He is the one experiencing the action.

Ham is the object form, like English him.

Compare:

• Han mister evnen — He loses the ability
• Jeg ser ham — I see him

Yes. It is grammatically complete:

• Han — subject
• mister — verb
• evnen — object

However, in real use it often depends on context. A listener may naturally wonder which ability is being lost. Norwegian often makes that explicit with til å + infinitive:

• Han mister evnen til å snakke
• Han mister evnen til å gå

So the short sentence is correct, but it can sound a little abstract if no context is given.

Because Norwegian usually marks definiteness with an ending on the noun.

Compare:

• en evne — an ability
• evnen — the ability

This pattern is very common:

• en bok → boken
• en bil → bilen

So in this sentence, -en already includes the idea of the.

Usually ability, but depending on context it can also mean capacity, capability, or even faculty in more formal English.

So the sentence may sound a little broad or abstract by itself. The exact nuance depends on the situation.

This is the normal Norwegian main-clause pattern:

subject + verb + object

• Han — subject
• mister — verb
• evnen — object

If you put another element first, Norwegian still keeps the finite verb in second position:

• Nå mister han evnen
• Plutselig mister han evnen

That verb-second pattern is a very important feature of Norwegian.

A simple learner-friendly guide is:

han MIS-ter EV-nen

A few points:

• Han has a broad a sound.
• mister has stress on the first syllable.
• evnen also has stress on the first syllable.
• evnen is two syllables, roughly EV-nen.

The exact sounds vary by dialect, but that stress pattern is a good starting point.