Jeg kan ikke løfte den tunge kuffert uden hjælp.

It breaks down like this:

• Jeg = I
• kan = can / am able to
• ikke = not
• løfte = lift
• den tunge kuffert = the heavy suitcase
• uden hjælp = without help

So the pattern is:

subject + finite verb + negation + infinitive + object + adverbial phrase

That is very normal Danish word order for a main clause.

Because kan is a modal verb, and after a modal verb Danish uses the bare infinitive.

So:

• Jeg løfter kufferten = I am lifting / I lift the suitcase
• Jeg kan løfte kufferten = I can lift the suitcase

In your sentence, the tense is carried by kan, so the main verb stays in infinitive form: løfte.

For the same reason: after modal verbs such as kan, vil, skal, må, bør, Danish normally uses the infinitive without at.

So:

• Jeg kan løfte den = correct
• Jeg kan at løfte den = incorrect

You do use at after many other verbs, for example:

• Jeg prøver at løfte den = I am trying to lift it

In a main clause, Danish usually places ikke after the finite verb.

Here, the finite verb is kan, so the order is:

• Jeg kan ikke løfte ...

Not:

• Jeg ikke kan løfte ... in a normal main clause

This is one of the most important Danish word-order rules.

A useful comparison:

• Main clause: Jeg kan ikke løfte den.
• Subordinate clause: ... fordi jeg ikke kan løfte den.

So in subordinate clauses, ikke often moves before the finite verb.

Because Danish forms definiteness differently when there is an adjective before the noun.

Compare:

• en kuffert = a suitcase
• kufferten = the suitcase
• en tung kuffert = a heavy suitcase
• den tunge kuffert = the heavy suitcase

So when a definite noun has an adjective in front of it, Danish normally uses:

den/det/de + adjective + noun

and not the suffixed definite form on the noun.

That is why den tunge kuffert is correct, not den tunge kufferten in standard Danish.

Because Danish adjectives change form depending on the noun phrase.

The adjective tung has forms like these:

• tung = common gender singular, indefinite
  
  • en tung kuffert
• tungt = neuter singular, indefinite
  
  • et tungt bord
• tunge = plural or definite
  
  • tunge kufferter
  • den tunge kuffert

In your sentence, the noun phrase is definite because of den, so the adjective takes the -e form: tunge.

Because kuffert is a common gender noun.

You can tell from the indefinite article:

• en kuffert = common gender
• et would mark a neuter noun

So with a definite phrase plus adjective, you get:

• den tunge kuffert

If the noun were neuter, you would use det:

• det tunge bord = the heavy table

So:

• den = common gender singular
• det = neuter singular
• de = plural

Here, den is functioning as a definite article, so it is basically part of the way Danish says the heavy suitcase.

It is not really the standalone pronoun it in this sentence.

That said, den can also be a pronoun in other contexts, and in some situations it can feel a bit like that if stressed. But in den tunge kuffert, the normal reading is simply the heavy suitcase.

Because hjælp here is being used as an abstract or uncountable idea, like English without help.

So:

• uden hjælp = without help

This is very natural Danish.

If you want to make it more specific, you can add something:

• uden din hjælp = without your help
• uden nogen hjælp = without any help

But in the original sentence, the plain form uden hjælp is exactly what you would expect.

Kan is the present tense form of the modal verb kunne.

So:

• Jeg kan ikke løfte den tunge kuffert uden hjælp. = present
• Jeg kunne ikke løfte den tunge kuffert uden hjælp. = past

English learners sometimes find this confusing because kunne can be both the dictionary form and a past form in different explanations, but the key point is:

• kan = present
• kunne = past / could

In a yes/no question, the finite verb comes first:

• Kan jeg ikke løfte den tunge kuffert uden hjælp?

If you move uden hjælp to the front for emphasis, Danish still keeps the finite verb in second position:

• Uden hjælp kan jeg ikke løfte den tunge kuffert.

This is the famous verb-second pattern in Danish main clauses. So even when something else comes first, the finite verb still stays in position 2.