Kit Kat doesn't have a hyphen.

Is KitKat one word or two?

According to the Hershey Kit Kat page, the proper form is, in fact, the split form of Kit Kat. However, Hershey's arch competitor Nestle manufactures and distributes KitKat in pretty much the rest of the world.

Is it KitKat or KitKat?

The origins of what is now known as the Kit Kat brand go back to 1911, when Rowntree's, a confectionery company based in York, England, trademarked the terms Kit Cat and Kit Kat.