På kontoret har vi mest arbejde om mandagen.

Because Danish has verb-second word order in main clauses.

If something other than the subject comes first, the finite verb usually comes second, and the subject comes after it.

So:

• Vi har mest arbejde om mandagen. = the subject vi comes first, so normal order is vi har
• På kontoret har vi mest arbejde om mandagen. = På kontoret is moved to the front, so the verb must come next: har, and then the subject vi

This is very common in Danish and is one of the first things English speakers need to get used to.

Starting with På kontoret puts focus on the location: at the office.

Danish often moves a time phrase, place phrase, or other element to the front to highlight it or set the scene. English can do this too:

• At the office, we have the most work on Mondays.

So the fronted phrase is not strange or poetic. It is perfectly normal everyday Danish.

In Danish, på is often used for workplaces, institutions, and locations where an activity happens, even where English might use in or at.

So på kontoret means at the office / in the office context.

Compare:

• på kontoret = at the office
• på skolen = at the school
• på arbejdet = at work

Using i kontoret would more strongly suggest physical position inside a particular room, and it often sounds less natural in this kind of general statement.

Kontoret is the definite form of kontor.

• et kontor = an office
• kontoret = the office

In Danish, the definite article is usually added to the end of the noun:

• en bil → bilen
• et hus → huset
• et kontor → kontoret

Here, på kontoret means at the office, referring to a specific office or the office in a general known sense.

Mest means most.

In this sentence, it means the greatest amount of work.

It is the superlative of meget:

• meget = much/a lot
• mere = more
• mest = most

So mest arbejde means the most work.

Because arbejde here is treated as an uncountable noun.

Use:

• mest with uncountable things:
  mest arbejde, mest tid, mest vand
• flest with countable plural things:
  flest bøger, flest kunder, flest opgaver

So:

• mest arbejde = the most work
• flest opgaver = the most tasks

English speakers often mix these up, because English uses most for both kinds.

Here it is a noun, meaning work.

That can be confusing because arbejde is also the infinitive form of the verb to work.

Compare:

• Vi har meget arbejde. = noun, We have a lot of work
• Vi arbejder meget. = verb, We work a lot

In your sentence, har makes it clear that arbejde is a noun: have work.

Because arbejde is being used as an uncountable mass noun, like work in English.

English says:

• We have a lot of work not
• We have a lot of a work

Danish works the same way:

• vi har meget arbejde
• vi har mest arbejde

So no et is needed here.

Om mandagen means on Mondays / on Monday in general and expresses something habitual or recurring.

This is a very common pattern in Danish:

• om mandagen = on Mondays
• om tirsdagen = on Tuesdays
• om sommeren = in summer / during the summer
• om aftenen = in the evening

The ending -en is the definite form, and in this kind of time expression it often gives the meaning of a regular pattern.

So om mandagen suggests that this is generally true on Mondays, not just one specific Monday.

These are important to keep apart:

• om mandagen = on Mondays, habitually / in general
• om mandag = sometimes used for on Monday, but less common in many everyday contexts than på mandag
• på mandag = next Monday

So in your sentence, om mandagen is the correct choice because it describes a repeated situation.

Examples:

• Vi har mest arbejde om mandagen. = We have the most work on Mondays.
• Vi ses på mandag. = See you on Monday / next Monday.

It means Mondays in general or typically on Mondays.

It does not always mean literally every single Monday without exception. It usually describes a normal pattern or tendency.

So the sentence suggests that Monday is generally the busiest day at the office.

Yes, that is grammatically fine.

That version has a more neutral word order:

• Vi har mest arbejde på kontoret om mandagen.

The original sentence:

• På kontoret har vi mest arbejde om mandagen.

puts more emphasis on På kontoret.

So the difference is mainly about focus and style, not basic meaning.

Time expressions often come later in Danish sentences, especially after the main content.

The sentence structure is very natural:

• place/topic first: På kontoret
• verb and subject: har vi
• object: mest arbejde
• time: om mandagen

Danish is fairly flexible, but this order sounds very normal.

Yes. Arbejde is often tricky for learners.

A rough guide is that it sounds something like AR-bai-də, but with very Danish vowel sounds and a softer ending than English speakers expect.

A few things to notice:

• the j helps create a sound like the y in eye
• the final -de is usually weak, not strongly pronounced
• the word is not pronounced exactly the way it looks to English speakers

If you are learning pronunciation, this is definitely a word worth listening to from native speakers several times.

It is completely natural everyday Danish.

Nothing in it sounds especially formal, literary, or old-fashioned. It is the kind of sentence you could easily hear in conversation or read in ordinary written Danish.