Hun låner min pumpe, når hendes dæk føles blødt om morgenen.

In Danish, the present tense is usually just verb + -r.

So:

• hun låner = she borrows / she is borrowing / she does borrow
• det føles = it feels / it is feeling like

Danish does not normally need an extra helper word like does in ordinary positive statements. The exact English translation depends on context. In this sentence, the meaning is habitual, so hun låner is best understood as she borrows.

For learners, the safest rule is:

• låne = borrow
• udlåne = lend

So Hun låner min pumpe means She borrows my pump.

In everyday speech, some Danes do use låne more loosely, but at learner level it is best to keep låne = borrow and udlåne = lend.

Because pumpe is a common-gender noun in Danish:

• en pumpe
• therefore min pumpe

If the noun were neuter and took et, you would use mit instead:

• et hus → mit hus

So the possessive changes with the gender of the noun:

• min
  • en-word
• mit
  • et-word
• mine
  • plural

This is a very common Danish question.

Sin/sit/sine is a reflexive possessive. It refers back to the subject of the same clause.

In the clause når hendes dæk føles blødt om morgenen, the grammatical subject is hendes dæk, not hun. Because of that, Danish does not use sin here.

So:

• Hun vasker sit hår. = She washes her own hair.
  Here hun is the subject of the same clause, so sit is used.

But in your sentence:

• Hun låner min pumpe, når hendes dæk føles blødt om morgenen.

Inside the når-clause, hun is not the subject, so hendes is correct.

Yes. Dæk can be confusing because the indefinite singular and indefinite plural can look the same.

• et dæk = a tire
• dæk = tires

In this sentence, we know it is singular because of the adjective:

• blødt = neuter singular
• if it were plural, it would be bløde

So:

• hendes dæk føles blødt = her tire feels soft
• hendes dæk føles bløde = her tires feel soft

Because dæk is a neuter noun: et dæk.

When an adjective is used with a neuter singular noun, it usually gets -t:

• et blødt dæk = a soft tire
• dækket er blødt = the tire is soft

That also happens when the adjective is a predicative adjective, after a verb like er, bliver, or føles.

Compare:

• en blød pude = a soft pillow
• puden er blød

but

• et blødt dæk = a soft tire
• dækket er blødt

Føles means feels in the sense of seems to feel or has the sensation/quality of.

So:

• Dækket føles blødt. = The tire feels soft.

This is different from føler, which usually means feels in the active sense:

• Hun føler dækket. = She feels/touches the tire.
• Hun føler sig træt. = She feels tired.

A useful contrast:

• Dækket føles blødt. = The tire feels soft.
• Hun føler på dækket. = She feels the tire with her hand.

So føles is the natural choice when the tire is the thing that feels soft.

Because når usually means when / whenever, especially for something repeated or expected.

This sentence describes a regular situation:

• whenever her tire feels soft in the morning, she borrows the pump

So når fits well.

Use hvis more for if, especially a more open or uncertain condition:

• Hvis hendes dæk føles blødt i morgen, låner hun min pumpe.
  = If her tire feels soft tomorrow, she’ll borrow my pump.

So:

• når = when / whenever
• hvis = if

Om morgenen means in the morning or in the mornings, often with a habitual or general sense.

That fits this sentence well, because the whole statement sounds like something that happens from time to time as a routine pattern.

Compare:

• om morgenen = in the morning / in the mornings
• i morges = this morning / earlier this morning

So:

• ... om morgenen = a general time frame
• ... i morges = one specific morning

Yes. Danish main clauses use verb-second word order, so if the subordinate clause comes first, the finite verb in the main clause comes before the subject.

Original order:

• Hun låner min pumpe, når hendes dæk føles blødt om morgenen.

With the når-clause first:

• Når hendes dæk føles blødt om morgenen, låner hun min pumpe.

Notice the change:

• not hun låner
• but låner hun

That inversion is very typical in Danish main clauses after a fronted element.

Yes. Danish often uses the present tense for habitual, general, and repeated actions.

So this sentence is not just about one single event. It describes a pattern:

• when that situation happens, she borrows the pump

That is why both verbs are in the present tense:

• låner
• føles

This is very similar to English sentences like:

• She borrows my pump when her tire feels soft in the morning.