Elektronikaffaldet står ved døren.

Because Danish, like German, often makes compound nouns by joining words together.

Here:

• elektronik = electronics
• affald = waste
• elektronikaffald = electronic waste
• elektronikaffaldet = the electronic waste

The last part of the compound is the main noun, so affald determines the basic meaning and grammar.

-et is the definite ending for a neuter singular noun in Danish. It works like English the.

So:

• elektronikaffald = electronic waste
• elektronikaffaldet = the electronic waste

Danish often adds the to the end of the noun instead of putting it in front.

Because in Danish, the definite article is usually attached to the noun.

Compare:

• English: the door

• Danish: døren

• English: the electronic waste
• Danish: elektronikaffaldet

A separate definite word such as det is used in some other structures, especially with adjectives, for example:

• det store hus = the big house

But in your sentence there is no adjective, so the ending on the noun is enough.

Grammatically, it is singular definite.

However, affald is often a mass noun, like trash or garbage in English. That means it can refer to a collection of things even though the grammar is singular.

So elektronikaffaldet can mean:

• the electronic waste as a category of stuff
• the pile/batch of electronic waste being referred to

Danish often uses position verbs where English simply uses is.

står literally means stands, but it is also used for things that are upright or placed somewhere in a standing position.

So:

• Elektronikaffaldet står ved døren = the electronic waste is standing / is placed by the door

This can sound natural if the waste is in a box, bag, bin, or some other upright arrangement.

English usually just says is, but Danish is more likely to choose:

• står = stands
• ligger = lies
• sidder = sits

depending on how something is positioned.

Yes, you could, but it is less specific.

• er ved døren means it is by the door
• står ved døren gives a stronger sense of physical placement, especially upright placement

So står is often more natural when talking about objects that have been put somewhere.

ved usually means by, near, or at.

So ved døren means:

• by the door
• near the door
• at the door

It does not usually mean in the doorway. If you wanted that idea, you might use a different expression.

Because døren means the door, while dør means a door or just door in a general sense.

So:

• dør = door
• døren = the door

In this sentence, it refers to a specific door, so the definite form is used.

The basic structure is:

• Elektronikaffaldet = subject
• står = verb
• ved døren = prepositional phrase

So the order is:

Subject + Verb + Place

This is a very normal Danish main-clause pattern.

You could say:

Der står elektronikaffald ved døren.

That means something like:

• There is electronic waste by the door.

Here:

• elektronikaffald is indefinite
• der står is a very common Danish way to introduce the existence of something somewhere

So the original sentence refers to specific electronic waste, while this version introduces it more generally.