It depends upon your comfort and ability as to what skis you want to use. Talking to BCMoffat about it, when people skijor at sled dog races, they use skate skis. They are also helping ski, not just are being pulled by the dog. But, they are only meant for groomed trails, and the person on them has to have a decent level of ski ability.
People do use classic cross country skis, but they are more useful with a slower dog and I've heard you may need a longer tug line to keep the dog off your skis as they are pointing into the dog more often than not.
Third option is metal edged skis.. but many associations warn against it as you could cut the dog. That said, some people prefer them as there is more stability to them and they can handle groomed and ungroomed trails. For a beginner without the balance for a skate ski, sometimes it is suggested to try a back country metal edged ski.
I've read that there are back country skis without metal edges.. best of both worlds, but I've never seen one. Then again, I teach downhill skiing, where if you don't have a metal edge you can't come play
So really it depends upon you, and what your goals are as to the type of ski you want to buy.