Learn Hardcore German: Trotz der langen Wartezeit erklärt die Ärztin freundlich, dass alles harmlos ist. - Despite the long waiting time, the doctor explains kindly that everything is harmless.

You may also hear trotz + dative in everyday speech (e.g., trotz der langen Wartezeit looks the same here, but with other nouns you’d see a difference), but genitive is the “safe” choice in writing.

How do I know it’s genitive and not dative here, since der can be both?

Good catch: der can mark several things. Here, the clue is the preposition trotz, which (in standard usage) signals genitive. Also, Wartezeit is feminine; its genitive singular article is der.

Why is it der langen Wartezeit with langen—what ending is that?

That’s the adjective ending for feminine genitive singular after a definite article (der).
Pattern: der + -en → der langen Wartezeit.

So:

die lange Wartezeit (nominative)
trotz der langen Wartezeit (genitive after trotz)

What role does Trotz der langen Wartezeit play in the sentence?

It’s a prepositional phrase used adverbially—basically a “despite…” phrase giving background circumstances. It’s not the subject or object; it modifies the main clause.

Why is the verb erklärt in second position even though the sentence starts with Trotz …?

German main clauses follow the V2 rule: the finite verb is in position 2.
When you front something (here: Trotz der langen Wartezeit), that whole phrase counts as position 1, so the verb still comes next:

1) Trotz der langen Wartezeit
2) erklärt
then the subject: die Ärztin …

Why does die Ärztin come after the verb—does that change meaning?

It’s mainly word order flexibility due to V2. Starting with Trotz … pushes the subject later. The meaning stays the same; it often just adds emphasis to what’s placed first (here: the “despite the long wait” idea).

What is the function of freundlich here—adjective or adverb?

It’s functioning as an adverb (more precisely: an adjective used adverbially) describing how she explains: she explains in a friendly way.

German often uses the same form for adjective/adverb (no -ly ending like in English).

Why is there a comma before dass, and do I always need it?

Yes, in standard German you must use a comma before a dass-clause because it introduces a subordinate clause:
… erklärt …, dass …

More generally, subordinate clauses are set off with commas.

Why is the verb at the end in dass alles harmlos ist?

Because dass introduces a subordinate clause, and in subordinate clauses the finite verb goes to the end (verb-final order).
So: dass … ist.

What exactly is alles grammatically—subject or object?

In the dass-clause, alles is the subject of ist.
Structure: alles (subject) + harmlos (predicative adjective) + ist (verb).

Why is harmlos not declined (no ending)?

Because harmlos is a predicative adjective after a linking verb (sein). Predicative adjectives in German do not take endings:

etwas ist harmlos (no ending)
vs.
ein harmloser Befund (attributive adjective with ending)

Is dass alles harmlos ist the direct object of erklären?

Yes—functionally it’s the content of what she explains, so it acts like a clausal object (often called an object clause / complement clause). You can think of it as “She explains that…”.