All Mora blades are in simple carbon steels or soft stainless, so diamonds not needed to sharpen them. If you want to get a diamond stone regardless, so it can handle your other knives in harder steels, that will of course handle any Mora blade too.
A factor worth considering that somebody mentioned above and I've run into recently: the pleasurable sharpening experience you get based on the tactile feedback from the stone. Water based stones tend to give you this a lot better than diamond stones, at least the ones I've tried. It's worth getting a nice, modest-priced water stone, and learning to freehand sharpen with it. And it's fun! I recently got
@FortyTwoBlades Arctic Fox, a 400-grit which is an aluminum oxide water stone that's perfect as an all-purpose one-grit sharpening stone. This is now my favorite all-purpose sharpening stone, and I use it on my own Mora carbon steel blade, and all my other kitchen knives, folders, utility knives, and outdoor-type knives in any type of carbon steel or softer/traditional stainless steels. For modern super hard steels like S30v/S35vn, M390, S90v/S110v, etc., you'd probably want to get something more optimized for cutting those, like a coarse diamond or a silicon carbide stone. But for
all other steels and general purpose sharpening, I don't think I've ever enjoyed sharpening as much as using the Arctic Fox.