Hvis billetkontoret er lukket, spørger jeg ved informationen i stedet.

Because Danish follows the V2 rule in main clauses: the finite verb usually comes in the second position.

The sentence starts with the if-clause:

Hvis billetkontoret er lukket

That whole clause takes the first position, so the main clause has to begin with the verb:

spørger jeg ved informationen i stedet

This is very common in Danish:

• Hvis han kommer, går vi.
• Når jeg har tid, ringer jeg.
• I morgen arbejder hun hjemme.

So after an opening clause or adverbial, Danish often switches from subject + verb to verb + subject.

Hvis means if.

It introduces a condition:

• Hvis billetkontoret er lukket = If the ticket office is closed

This is the normal word for a real condition in Danish. It is used much like English if.

Compare:

• Hvis det regner, bliver vi hjemme. = If it rains, we stay home.
• Hvis du vil, kan jeg hjælpe. = If you want, I can help.

Billetkontoret means the ticket office.

It is made up of:

• billet = ticket
• kontor = office
• -et = the definite ending for a neuter noun

So:

• et billetkontor = a ticket office
• billetkontoret = the ticket office

Danish often forms compound nouns as one single word, much more than English does. So where English has ticket office, Danish has billetkontor.

Er lukket means is closed.

This describes a state, not an action:

• er = is
• lukket = closed

So the sentence means the ticket office is already in the state of being closed.

Compare:

• Butikken lukker kl. 18. = The shop closes at 6 p.m.
  This is an action/event.
• Butikken er lukket. = The shop is closed.
  This is a state.

In your sentence, the state is what matters: if the office is closed, the speaker will ask somewhere else.

Because Hvis billetkontoret er lukket is a subordinate clause, and in standard Danish writing it is separated from the main clause with a comma.

So the structure is:

• subordinate clause: Hvis billetkontoret er lukket
• main clause: spørger jeg ved informationen i stedet

Danish comma rules can be a little tricky, but in a sentence like this, the comma is exactly what you should expect.

Here ved informationen means something like at the information desk or at information.

The parts are:

• ved = at / by / near
• informationen = the information desk/office/service point

So the idea is: if the ticket office is closed, the speaker asks at the information desk instead.

A useful note: in real-life Danish, people may also say things like:

• i informationen
• ved informationsskranken

depending on the exact place. But in this sentence, ved informationen means the speaker goes to the information point to ask there.

Because Danish usually puts the definite article at the end of the noun.

So:

• information = information / information desk
• informationen = the information / the information desk

This is one of the biggest differences from English. Instead of the + noun, Danish often uses noun + ending:

• bogen = the book
• huset = the house
• kontoret = the office
• informationen = the information desk / the information

Here, the exact English translation depends on context. In this sentence, it clearly refers to the place or desk, not abstract information.

I stedet means instead.

It shows that one action happens as an alternative to another:

• Hvis billetkontoret er lukket, spørger jeg ved informationen i stedet.
• If the ticket office is closed, I ask at the information desk instead.

You can think of it as replacing the first option with another one.

More examples:

• Vi tager bussen i stedet. = We’ll take the bus instead.
• Hun drikker te i stedet for kaffe. = She drinks tea instead of coffee.

Because Danish often uses the present tense to talk about the future, especially when the context already makes the future meaning clear.

So:

• spørger jeg literally looks like I ask
• but in context it can naturally mean I’ll ask

The condition introduced by hvis makes it clear that this is about what the speaker will do in that situation.

This is very normal in Danish:

• I morgen rejser vi. = We’re leaving tomorrow.
• Hvis han ringer, kommer jeg. = If he calls, I’ll come.

So you do not always need a special future form in Danish.

Yes. Danish often allows så in sentences like this:

• Hvis billetkontoret er lukket, så spørger jeg ved informationen i stedet.

This can make the structure feel a bit more explicit, similar to English then. But it is not necessary. The version without så is completely normal.

The sentence has two parts:

1. Hvis billetkontoret er lukket
   = a conditional subordinate clause
   = If the ticket office is closed

2. spørger jeg ved informationen i stedet
   = the main clause
   = I ask at the information desk instead

So the overall pattern is:

Hvis + condition, verb + subject + rest

That is a very common Danish pattern, and it is worth learning as a chunk.