Learn Hardcore German: Ich klebe mir einen Notizzettel mit der Deadline der Abgabe an den Laptopständer. - I stick a little note with the submission deadline onto the laptop stand.

it’s still grammatical, but it sounds less personal and less like it’s specifically for you. The version with mir emphasizes that it’s your reminder.

Why is it einen Notizzettel and not ein Notizzettel or einem Notizzettel?

Notizzettel is masculine (der Notizzettel). In the sentence it is the direct object, so it must be in the accusative case.

Masculine indefinite article:

Nominative: ein Notizzettel (as subject)
Accusative: einen Notizzettel (as direct object)
Dative: einem Notizzettel
Genitive: eines Notizzettels

Here we have:

Subject (nominative): Ich
Indirect object (dative): mir
Direct object (accusative): einen Notizzettel

So einen is required by the grammar (masculine + accusative).

Why is it an den Laptopständer and not an dem Laptopständer?

An is a so‑called two-way preposition (Wechselpräposition) in German. It can take either:

dative (location – where?)
accusative (direction – to where?)

In your sentence, there is movement towards the laptop stand: you are sticking the note onto it.

Ich klebe … an den Laptopständer.
→ movement to the stand → accusative → den Laptopständer

If it were only describing location (no movement), you would use dative:

Der Notizzettel hängt an dem / am Laptopständer.
→ the note is hanging on the stand → dative → dem Laptopständer

So:

an den = onto the (direction, accusative)
an dem / am = on the (location, dative)

Why does mit der Deadline use der? Isn’t Deadline feminine?

Yes, Deadline is feminine in German (die Deadline).

The preposition mit always takes the dative case. For feminine nouns in the singular, nominative and dative both look like der in the article table:

Feminine singular (die Deadline):

Nominative: die Deadline
Accusative: die Deadline
Dative: der Deadline
Genitive: der Deadline

After mit, you must use dative:

mit der Deadline – with the deadline

So der here is dative feminine, not nominative.

What is der Abgabe doing after Deadline? Why is that also der?

In mit der Deadline der Abgabe, the phrase der Abgabe is a genitive phrase that describes Deadline:

die Deadline der Abgabe
= the deadline of the submission

Abgabe is feminine (die Abgabe). Its singular forms:

Nominative: die Abgabe
Accusative: die Abgabe
Dative: der Abgabe
Genitive: der Abgabe

So der Abgabe here is genitive singular → of the submission.

Both dative and genitive feminine singular use der, but the function is different:

mit der Deadline → dative (object of mit)
der Abgabe → genitive (possessor of Deadline)

Could I say mit der Deadline für die Abgabe instead of mit der Deadline der Abgabe?

Yes, both are possible, but they differ slightly in style:

mit der Deadline der Abgabe
– literally with the deadline of the submission (more compact, a bit more formal/typical written style)
mit der Deadline für die Abgabe
– with the deadline for the submission (more explicit because of für; sounds very natural, maybe a bit more conversational)

Grammatically:

für takes accusative → für die Abgabe
der Abgabe is genitive.

You can use either; both are idiomatic.

Why is the order mir einen Notizzettel and not einen Notizzettel mir?

When you have both a dative object and an accusative object in German, and both are nouns or one is a pronoun, the usual order is:

dative → accusative

So:

Ich klebe mir einen Notizzettel …
(dative mir before accusative einen Notizzettel)

You could, in theory, say Ich klebe einen Notizzettel mir …, but that is unusual and would sound marked or awkward in everyday speech. Native speakers almost always say:

Ich klebe mir einen Notizzettel …

Is mir a reflexive pronoun here, like in Ich wasche mich?

No, mir here is not reflexive in the usual sense.

In Ich wasche mich, mich is a true reflexive pronoun: you wash your own body.

In Ich klebe mir einen Notizzettel …, mir is a dative of benefit (sometimes called reflexive dative):

You are not sticking the note onto yourself.
You are sticking a note (accusative) onto the stand for your own benefit (dative mir).

Compare:

Ich kaufe mir ein Buch. – I buy myself a book.
Ich ziehe mir eine Jacke an. – I put a jacket on (myself).

Same pattern: mir shows who benefits, but the object being acted on is something else (einen Notizzettel, ein Buch, eine Jacke).

Why is an used here? In English I’d say “onto” or “on”. What’s the nuance of an?

In German, an often corresponds to English on / onto / at, especially for vertical surfaces or edges.

Ich klebe den Zettel an die Wand. – I stick the note onto the wall.
Ein Poster hängt an der Tür. – A poster is hanging on the door.

In your sentence:

an den Laptopständer → onto the laptop stand

If you imagine sticking the note to a vertical part or an edge of the stand, an is the natural choice. For placing something flat on a horizontal surface, German more often uses auf:

Ich lege das Buch auf den Tisch. – I put the book on(‑to) the table.

So here an is correct because the idea is “attached on the side / front of the stand”, not lying on top of it.

Why is the prepositional phrase an den Laptopständer at the end? Could it go somewhere else?

In a simple German main clause, the typical order is:

Subject – Verb – (objects & adverbials) – rest – [final position for extra info]

The “where to” phrase an den Laptopständer is a kind of adverbial of place/direction, and such phrases very often appear towards the end of the clause:

Ich klebe mir einen Notizzettel … an den Laptopständer.

You can move it, especially for emphasis, but the neutral, most natural place is at the end. Possible variants:

Ich klebe mir an den Laptopständer einen Notizzettel mit der Deadline der Abgabe.
(still correct, slightly marked word order)

The main rule you must respect:

The finite verb (klebe) stays in second position.
The rest is quite flexible, but the version in your sentence is the most idiomatic.

What exactly is Laptopständer? How is its gender decided?

Laptopständer is a compound noun:

Laptop
- Ständer → Laptopständer

In German compounds, the last part decides the gender and plural:

der Ständer (stand, holder) → masculine
→ der Laptopständer (also masculine)

Therefore:

Nominative singular: der Laptopständer
Accusative singular: den Laptopständer

That’s why the sentence uses an den Laptopständer (accusative masculine).

What’s the difference between Notizzettel and Notiz?

Both relate to “notes”, but they’re used slightly differently:

die Notiz – the note as the information or short written remark
- Ich mache mir eine Notiz. – I make a note (for myself).
der Notizzettel – literally a note slip / sticky note; a piece of paper with a note on it
- Ich klebe mir einen Notizzettel an den Laptopständer. – I stick a (small) note (on paper) onto the laptop stand.

You could say:

Ich schreibe mir eine Notiz auf einen Notizzettel.
– I write myself a note on a slip of paper.

In your sentence, since you are physically sticking a piece of paper, Notizzettel is the natural choice.