Hun virker træt i dag.

Virker means seems or appears here. It suggests an impression, not a definite fact.

• Hun virker træt i dag. = She seems tired today.
• Hun er træt i dag. = She is tired today.

So virker is softer and more observational than er.

Virker is the present tense of virke.

A useful pattern in Danish is that the present tense is often formed by adding -r to the infinitive:

• virke → virker

Unlike English, Danish verbs do not change according to the subject:

• jeg virker
• du virker
• hun virker
• vi virker

So hun virker is not a special she form; it is just the normal present tense.

In this sentence, virke means to seem / to appear.

That is one common use of the verb:

• Han virker glad. = He seems happy.
• Det virker svært. = It seems difficult.

So in Hun virker træt i dag, the verb connects the subject to an impression about her condition.

Because træt is describing hun, which is singular.

Here træt is a predicate adjective after the linking verb virker. In Danish, predicate adjectives can agree with the subject. For træt, the singular form is træt, while the plural form is trætte:

• Hun virker træt. = She seems tired.
• De virker trætte. = They seem tired.

So trætte would be used for a plural subject, not hun.

It is an adjective.

It describes hun, not the verb itself. In other words, it tells us what she seems like. This is very common after verbs such as:

• være = to be
• blive = to become
• virke = to seem
• se ud = to look

So træt is functioning as a predicative adjective.

I dag is a fixed Danish time expression meaning today.

Literally, i often means in, but in this phrase the whole expression is best learned as a unit:

• i dag = today
• i morgen = tomorrow

You do not normally add an article here. It is just the standard idiomatic way to say today in Danish.

Yes. Danish allows some flexibility with time expressions.

The most neutral version is:

• Hun virker træt i dag.

You can also front it for emphasis:

• I dag virker hun træt.

When you move i dag to the beginning, Danish uses verb-second word order, so the verb virker comes before the subject hun.

Both are correct, but they have slightly different emphasis.

The structure is:

• Hun = subject
• virker = verb
• træt = subject complement / predicative adjective
• i dag = time expression

So the pattern is basically:

Subject + verb + complement + time expression

This is a very common Danish sentence pattern.

Yes. Virke can also mean to work / to function.

For example:

• Maskinen virker. = The machine works.

But in Hun virker træt i dag, it does not mean works. Because it is followed by an adjective (træt), the meaning is clearly seems / appears.

You usually place ikke after the finite verb:

• Hun virker ikke træt i dag. = She does not seem tired today.

That placement is very typical in Danish main clauses:

• subject + finite verb + ikke
  • rest

So ikke normally comes after virker here.