Knappen sidder løst på min skjorte.

Because knappen is the definite form of knap.

• en knap = a button
• knappen = the button

Danish usually adds the definite article to the end of the noun instead of putting a separate word before it. So -en here means the.

Sidder is the present tense of sidde.

A very common pattern in Danish is:

• infinitive: sidde
• present: sidder

So grammatically, sidder is the finite verb of the sentence.

Because sidde is not only used for people who are sitting. In Danish, it is also often used for things that are positioned, attached, or sitting in place.

So a button, label, picture, or stain can all sidde somewhere.

Here, sidder suggests that the button is attached to the shirt, but not firmly.

Løst tells you how the button is attached. In English terms, it works like loosely.

It comes from the adjective løs = loose, but here it is used in an adverb-like way:

• løs = loose
• løst = loosely / in a loose way

So sidder løst is a very natural combination for something that is not fastened tightly.

Yes, that can also be natural, but the nuance is a little different.

• er løs = describes the button's condition: it is loose
• sidder løst = describes the way it is attached: it sits loosely

In many situations, both are possible. Sidder løst is especially idiomatic when talking about how firmly something is fastened.

Because på is the normal preposition for something attached on or onto the surface of something.

A button is attached på a shirt, not i it.

So:

• på skjorten = on the shirt
• i skjorten would suggest something inside the shirt, which is not what is meant here

Because skjorte is a common-gender noun, an en-word:

• en skjorte

For singular possessives:

• min
  • common gender
• mit
  • neuter
• mine
  • plural

So:

• min skjorte
• mit hus
• mine skjorter

Because when a possessive like min, din, hans, hendes, and so on comes before the noun, the noun normally stays in its indefinite form.

So Danish says:

• min skjorte

not:

• min skjorten

This is a very important pattern in Danish.

Yes. Danish is a V2 language, which means the finite verb usually stays in second position.

The basic sentence is:

• Knappen sidder løst på min skjorte.

But you can move another element to the front for emphasis:

• På min skjorte sidder knappen løst.

Notice what happens: when På min skjorte moves to the front, the verb sidder still stays in second position, and the subject knappen comes after it.

It is:

• Knappen = subject
• sidder = verb
• løst = adverb-like description of how it sits
• på min skjorte = prepositional phrase telling where

So the sentence follows a very common Danish pattern:

subject + verb + other information