Learn Hardcore Norwegian: Når jeg våkner etter en lang drøm, kan jeg fortsatt lukte kaffe på kjøkkenet. - When I wake up after a long dream, I can still smell coffee in the kitchen.

når is used for general, habitual or future events and for asking about time (e.g. “Når begynner timen?” – “When does class start?”).
da refers to a specific, completed moment in the past (e.g. “Da jeg våknet i morges, var det snø” – “When I woke up this morning, it was snowing”).
In your sentence, når signals “whenever/when I wake up” rather than one single past event.

Why is våkner in the present tense, even though the dream already happened?

Using the simple present (våkner) makes the statement general or immediate: “Whenever I wake up after a long dream…”. If you wanted to describe one past occasion, you’d switch to past tense with da:
“Da jeg våknet etter en lang drøm, luktet jeg fortsatt kaffe…”

Why does the main clause say kan jeg fortsatt lukte instead of jeg kan fortsatt lukte?

When a subordinate (or adverbial) clause (Når jeg våkner …) kicks off the sentence, the following main clause often inverts subject and finite verb. The finite verb (kan) comes first, then the subject (jeg). This inversion is a standard V2-phenomenon triggered by fronting the subordinate clause.

Is the comma after drøm mandatory?

In written Norwegian, you normally place a comma between an introductory subordinate clause and the main clause that follows. It enhances clarity, especially in longer sentences, though very short clauses sometimes drop it.

Why is it en lang drøm (indefinite) but kjøkkenet (definite)?

en lang drøm refers to “any long dream” (indefinite singular common gender).
kjøkkenet (“the kitchen”) is definite because you’re referring to a specific place in your home.

Why does the adjective lang have no ending (not lange or langt)?

In Bokmål, drøm is a common-gender noun in the indefinite singular, so the adjective stays in its basic form: en lang drøm.
If it were a neuter noun (et), you’d add -t (e.g. et stort hus). If it were plural, you’d add -e (e.g. lange drømmer).

Can I swap fortsatt with fremdeles?

Yes. Both mean “still.”

fortsatt is slightly more common in everyday speech.
fremdeles is equally correct and maybe a bit more formal or literary.

Why is lukte followed directly by kaffe with no preposition?

Lukte (to smell) is transitive when you smell something: you smell coffee (lukte kaffe).
If you want “to smell of/like something,” you’d use lukte av: “Rommet lukter av maling” (“The room smells of paint”).

Why use på kjøkkenet rather than i kjøkkenet?

In Norwegian you normally say på with rooms and public spaces (e.g. på kjøkkenet, på skolen, på kontoret), even though English uses “in.”