These are question words that translate the English WHICH
Hvilken is, in general, used to single out one object among many.
These question words agree with the noun’s gender and number:
Hvilken pakke sender du?
Which parcel do you send?
Hvilk -en in front of a masculine noun (en pakke)
Hvilken avis leser du?
Which newspaper do you read?
Hvilk -en in front of a feminine noun (ei avis)
Hvilket bord vil du ha?
Which table do you want?
Hvilk -et in front of a neuter noun (et bord)
Hvilke aviser leser du?
Which newspapers do you read?
Hvilk -e in front of plural nouns (aviser)
You use Hvilken- Hvilket-Hvilke as question words in normal questions but you have to remember to match them with the gender of the noun you are attaching them to.