The term "premium" is purely a marketing term....which is best off ignored in favor of facts.
Depends on which engine you have and how octane is labeled in your locale.
The 80 hp 912 is a lower compression engine and can use 87 octane
The 100 hp 912ULS requires a minimum of 91 octane
With the octane being determined by the average value of the two methods of determining octane - research and motor, which you should see on the dispensing pump as R + M/2 = 87 or 91 (be aware there is other labeling which uses only one of the methods and the numbers come out differently)
OK now the corn gas thing - Rotax permits up to 10% ethanol as far as the engine is concerned; however, you have to consider the entire fuel system. Kitfoxes use fiberglass tanks and I believe the consensus is fiberglass tanks can degrade with the use of ethanol. I have a friend with a different plane which has poly fuel tanks and he runs 91 octane corn gas all the time because the entire system is compatible up to 10% ethanol.
Having a 912ULS in our kitfox, I use 91 corn free autogas, occasionally 100LL when on a trip when that is all a person can get. The autogas is also procured from a site which has a dedicated tank and pump for that product.
One word to the wise - some (getting to be more all the time) auto fuel stations do not have a dedicated 91 octane pumps; but, use blend valves drawing from different grades of fuel all going through one hose and pump - this means the first gallon, even if you select 91 corn free, has a pretty good chance of being diluted wItith lower grade or ethanol contaminated junk. I have no idea how often blend valves can fail but I am not at all in favor of getting airplane fuel from any place which uses multiple tanks and a blend valve. One gallon of 87 in a 5 gallon container of gas (or a gallon of E85) which you want 91 octane in could very well inspire detonation in a 912ULS as the 91 is a hard minimum. I do know of folks who squirt the first couple gallons in their car then fill their aircraft cans.