Du er alltid velkommen her.

You can approximate it in English as
“doo air AHL-teed VEL-koh-men hair.”
Breakdown:
• Du – /dʉː/ (like French u or German ü)
• er – /ær/ (similar to English air, short e)
• alltid – /ˈɑlːtiːd/ (double l is long, tid rhymes with “teed”)
• velkommen – /ˈvɛlkɔmən/ (stress on vel-)
• her – /heːr/ (long e, like “hair” but more closed)

In Norwegian main clauses, adverbs of frequency/time like alltid normally follow the finite verb. The typical word order is:
Subject – finite verb – adverb of frequency – complement
So Du (subject) + er (verb) + alltid (adverb) + velkommen her (complement).

Velkommen here is an adjective agreeing with a singular common-gender subject (du). Norwegian adjective endings:
• Indefinite singular common – no ending → velkommen
• Indefinite singular neuter – add -t → velkomment (e.g., et velkomment tiltak)
• Indefinite plural – add -e → velkomne (e.g., gjestene er velkomne)
Since du is singular, you use velkommen.

• Her indicates a static location (“right here”).
• Hit indicates movement toward here (“come here”).
In Du er alltid velkommen her, you’re talking about being welcome in this place (no movement), so you use her.

Invert the finite verb and the subject:
Er du alltid velkommen her?
That means “Are you always welcome here?”

Use the plural pronoun dere and the plural adjective ending -e:
Dere er alltid velkomne her
That means “You (all) are always welcome here.”

The formal singular pronoun is De (capital D in writing). You would say:
De er alltid velkommen her
Question form by inversion: Er De alltid velkommen her?
Note that formal De is quite rare in modern spoken Norwegian; most people just use du.

You can insert words like hjertelig or varmt before velkommen:
Du er alltid hjertelig velkommen her
Du er alltid varmt velkommen her
Hjertelig velkommen (“heartily welcome”) is especially common when you want to sound especially sincere.