Når dagen er så travel, tør jeg nesten ikke tenke på hvor mye som fortsatt må gjøres.

Yes, this is a very common point of confusion.

In Norwegian, travel is an adjective meaning busy, hectic, or rushed. It is not the same word as the English verb/noun travel.

So:

• en travel dag = a busy day
• jeg har det travelt = I’m busy

In this sentence, så travel means so busy or this busy.

Når usually means when, and sometimes whenever, depending on context.

Here it introduces a time/circumstance clause:

• Når dagen er så travel ... = When the day is so busy ...

A natural English rendering might also be:

• When the day is this busy ...
• On a day this busy ...

So Når is setting the situation for the rest of the sentence.

This is because of normal Norwegian main-clause word order.

Norwegian follows the V2 rule in main clauses: the finite verb must come in the second position.

The opening clause Når dagen er så travel takes the first position, so the finite verb of the main clause must come next:

• Når dagen er så travel, tør jeg nesten ikke tenke ...

If you remove the opening clause, you get the more basic order:

• Jeg tør nesten ikke tenke ...

So the inversion tør jeg happens because something else has been placed first.

Tør is the present tense of å tørre, which means to dare.

In Norwegian, tørre often behaves like a modal verb, so it is commonly followed by an infinitive without å:

• Jeg tør ikke spørre = I don’t dare ask
• Hun tør ikke gå = She doesn’t dare go

So:

• tør jeg nesten ikke tenke = I hardly dare think

You may also sometimes see å after tørre, but leaving it out is very common and completely natural.

Literally, nesten ikke means almost not, but in natural English it usually comes out as hardly.

So:

• jeg tør nesten ikke tenke på ...
  = I hardly dare think about ...

This is slightly softer than a full ikke:

• jeg tør ikke = I do not dare
• jeg tør nesten ikke = I almost do not dare / I hardly dare

It suggests the speaker feels overwhelmed.

Because tenke på is the normal expression for think about something.

Compare:

• tenke = to think
• tenke på noe = to think about something

Examples:

• Jeg tenker. = I am thinking.
• Jeg tenker på deg. = I’m thinking about you.

So in this sentence:

• tenke på hvor mye ... = think about how much ...

Så is an intensifier here. It means so or this in the sense of degree.

So:

• så travel = so busy
• så stor = so big
• så vanskelig = so difficult

In this sentence, så travel suggests a high degree:

• When the day is so busy / this busy ...

It is not the same as English so in every situation, but here the match is very close.

Because Norwegian is referring to the specific day/situation at hand, not just any busy day in general.

• dagen = the day
• en dag = a day

So:

• Når dagen er så travel ... means something like When the day is this busy ...
• Når en dag er så travel ... would sound more general and less natural here

Using the definite form makes it feel like the speaker is talking about the actual day they are in the middle of.

This is a very common Norwegian pattern.

After expressions like hvor mye, hvor mange, hvor lite, and similar forms, Norwegian often uses som before the rest of the clause:

• Jeg vet hvor mange som kommer = I know how many are coming
• Hun så hvor mye som gjensto = She saw how much remained

So:

• hvor mye som fortsatt må gjøres = how much still has to be done

The som usually does not get translated directly into English here, but it is natural and expected in Norwegian.

Må gjøres is a passive construction meaning must be done.

Breakdown:

• må = must
• gjøres = be done

The verb gjøres is the passive form of gjøre.

So:

• hvor mye som fortsatt må gjøres = how much still must be done

This is a very common way to express that something needs doing, especially in neutral or written-style Norwegian.

Because fortsatt means still, and in subordinate clauses Norwegian often places adverbs before the finite verb.

Here the clause is:

• som fortsatt må gjøres

That word order is normal in a subordinate clause.

Compare the general idea:

• main clause: Det må fortsatt gjøres mye
• subordinate clause: ... hvor mye som fortsatt må gjøres

So this sentence is also useful for seeing that Norwegian subordinate clauses often have different word order from English.