Nach der Rückgabe bewahre ich die Rückgabequittung auf.

Because nach is a preposition that takes the dative case when it means after.

• Base noun: die Rückgabe = the return
• Dative singular: der Rückgabe

So:

• nach der Rückgabe = after the return

This is very common in German:

• nach dem Essen = after the meal
• nach der Arbeit = after work
• nach dem Unterricht = after class

Here, nach means after in a time sense.

So nach der Rückgabe means after the return or once the item has been returned.

Be careful: nach has several meanings in German depending on context, for example:

• to or toward with cities/countries: Ich fahre nach Berlin
• according to: nach dem Gesetz
• after in time: nach der Rückgabe

In this sentence, it is clearly the time meaning: after.

Because the verb is aufbewahren, which is a separable verb.

• Full infinitive: aufbewahren = to keep, to store, to retain
• In a main clause, the prefix often separates:
  • Ich bewahre ... auf.

So:

• bewahre = main verb part
• auf = separated prefix

That is why the sentence is:

• Nach der Rückgabe bewahre ich die Rückgabequittung auf.

and not:

• Nach der Rückgabe aufbewahre ich ... ❌

But in the infinitive or with a modal, it stays together:

• Ich möchte die Rückgabequittung aufbewahren.

German main clauses usually follow the verb-second rule, often called V2.

That means the conjugated verb must be in the second position. The first position can be taken by different elements, not just the subject.

Here, Nach der Rückgabe is placed first for emphasis or to set the time frame. Then the conjugated verb must come next:

• Nach der Rückgabe = position 1
• bewahre = position 2
• ich = then comes the subject

So this is completely normal German word order.

You could also say:

• Ich bewahre die Rückgabequittung nach der Rückgabe auf.

That is also grammatical, but the original sentence emphasizes when this happens right away.

It is the direct object of the verb aufbewahren, so it is in the accusative case.

The thing being kept is the return receipt, so that noun is the object:

• Ich bewahre was auf?
• die Rückgabequittung

Since Rückgabequittung is feminine, the accusative singular article is die.

For feminine nouns:

• nominative: die
• accusative: die

So the form looks the same, but the function is different.

Yes. German often combines several nouns into one compound noun.

Here:

• Rückgabe = return
• Quittung = receipt

Together:

• Rückgabequittung = return receipt / receipt for the return

In German, the last part usually determines the grammatical gender and the general category of the word.

Since die Quittung is feminine, die Rückgabequittung is also feminine.

This kind of compounding is extremely common in German.

Not exactly.

aufbewahren usually means:

• to keep
• to store
• to retain for later
• to hold onto something carefully

In this sentence, it suggests keeping the receipt in case it is needed later.

behalten usually means:

• to keep something instead of giving it back
• to continue to have something

Compare:

• Ich bewahre die Quittung auf.
  = I keep/store the receipt.

• Ich behalte die Quittung.
  = I keep the receipt.

Both can sometimes work in English as keep, but aufbewahren more strongly suggests storing or saving it, often for a practical reason.

Because they are nouns, and in German all nouns are capitalized.

So in this sentence:

• Rückgabe is a noun
• Rückgabequittung is a noun

That is why they begin with capital letters.

This is a very important spelling rule in German and helps learners identify nouns more easily.

Yes, you could say that, but it sounds a bit different.

• nach der Rückgabe = after the return
• nach dem Zurückgeben = after returning it

The first uses a noun: die Rückgabe.
The second uses a verbal noun / nominalized infinitive: das Zurückgeben.

Both are possible, but nach der Rückgabe sounds compact and natural, especially in formal or written contexts.

It sounds neutral to slightly formal.

Why?

• Rückgabequittung is a precise compound noun.
• aufbewahren sounds a bit more careful and formal than very casual alternatives.

In everyday speech, someone might also say something like:

• Nach der Rückgabe hebe ich den Beleg auf.

That sounds a little more conversational, depending on region and context.

But the original sentence is completely natural and correct.