So is it ski joring, skijoring, or ski-joring?
Take your pick. Merriam-Webster's Collegiate Dictionary (Tenth Edition) lists it as one word, from the Norwegian skikjøring (ski plus kjøring, or "driving").
On the North American Ski Joring Association's web site, it's two words. I have also seen the term hyphenated on event posters, announcements, etc.
For this article, I decided to go with the dictionary version. --L.L.R.