När hon nyser, håller hon handen framför näsan.

När means when in the sense of time.

Here it introduces a time clause: När hon nyser = When she sneezes.

A learner might wonder about om, but om usually means if, not when. So:

• När hon nyser = when she sneezes
• Om hon nyser = if she sneezes

Since the sentence describes what happens at the time she sneezes, när is the correct choice.

This is because Swedish uses V2 word order in main clauses. That means the finite verb must come in the second position.

The first part, När hon nyser, is a subordinate clause. When that whole clause comes first, the main clause still has to follow V2 order:

• När hon nyser, håller hon handen framför näsan.

So the structure is:

• first position: När hon nyser
• second position: håller
• then subject: hon

If you said När hon nyser, hon håller..., that would sound wrong in standard Swedish.

Nyser is the present tense of the verb nysa = to sneeze.

So:

• att nysa = to sneeze
• hon nyser = she sneezes / she is sneezing

In Swedish, the present tense often covers both simple present and present progressive meanings, depending on context.

Håller is the present tense of hålla = to hold.

So:

• att hålla = to hold
• hon håller = she holds / she is holding

Here it describes what she does when she sneezes.

In Swedish, body parts are often expressed with the definite form instead of a possessive like her.

So Swedish commonly says:

• hon tvättar händerna = literally she washes the hands
• han stänger ögonen = literally he closes the eyes
• hon håller handen framför näsan = literally she holds the hand in front of the nose

In natural English, you usually say her hand and her nose, but Swedish often leaves that possession understood from the subject.

Because Swedish often does not use possessives with body parts when the owner is obvious.

So handen and näsan already sound natural here.

You could use a possessive in some contexts, but it would usually add emphasis or contrast:

• hon håller sin hand framför näsan = she holds her own hand in front of her nose
• hon håller hennes hand framför näsan = she holds her hand in front of the nose, where her refers to some other female person

In this sentence, simple handen and näsan are the most natural choice.

Framför means in front of or before, depending on context.

Here it means in front of:

• framför näsan = in front of the nose

So the image is that she places her hand before her nose when she sneezes.

Because framför näsan expresses the idea that the hand is positioned in front of the nose, not directly on it or over it.

Compare:

• framför näsan = in front of the nose
• på näsan = on the nose
• över näsan = over the nose

If someone sneezes into their hand, framför näsan is the natural expression for placing the hand in front of the nose.

It can mean either, depending on context.

Swedish present tense often covers both:

• a habitual action: When she sneezes, she holds her hand in front of her nose
• an action described as part of a scene: When she sneezes, she is holding her hand in front of her nose

Without extra context, this sentence is most naturally understood as a general or habitual action.

The comma is possible and natural, but in modern Swedish punctuation it is often optional, especially in short sentences.

So both of these can be seen:

• När hon nyser, håller hon handen framför näsan.
• När hon nyser håller hon handen framför näsan.

The comma helps show the boundary between the subordinate clause and the main clause, so many learners find it useful.

A close breakdown is:

• När = when
• hon = she
• nyser = sneezes
• håller = holds
• hon = she
• handen = the hand
• framför = in front of
• näsan = the nose

So very literally:

When she sneezes, holds she the hand in front of the nose.

That sounds unnatural in English, but it helps show how the Swedish sentence is built.

Yes, that is grammatically possible, but it sounds less natural in an ordinary sentence.

Using sin hand and sin näsa makes the possession more explicit than Swedish usually needs with body parts. Native speakers would normally prefer:

• När hon nyser, håller hon handen framför näsan.

Your version is understandable, but it may sound a bit heavy or overly specific unless you are emphasizing that it is her own hand and her own nose.

Because the sentence has two clauses:

• När hon nyser = subordinate clause
• håller hon handen framför näsan = main clause

Each clause needs its own subject if the subject is stated. So Swedish repeats hon, just like English repeats she:

• When she sneezes, she holds her hand in front of her nose.

You cannot leave out the second hon here.