I don't speak Norwegian, but I think I was able to get the basic meaning of the text, based on similarities with other languages - and a lot of guessing. But then again, I could be wrong. If you speak Norwegian, please feel free to make any corrections.
The message on the back of the card seems to be wishing Johan a happy Christmas, though by the time he receives the card the holiday has already passed. It looks as if the card was sent on the 7th of December, 1911 and didn't arrive at its destination until a month later.
The message wishes Johan a happy Christmas and appears to be from his sister, Alma Hansen, who says "Here you see my son Karl."