I imagine most varieties of corn would work, especially the more fibrous types, because they have less water content. I don't know anything about Japanese black corn specifically, but it around work.

To make the corn meal, you take it off the cob, dehydrate it in an oven or dehydrator, and run it through a food processor, blender, or grain mill. Put it through a small sifter to remove any hulls, then grind it again. You can do it a 3rd time for a finer powder.

As far as the cookies go, there's a bunch of recipes out there. Any corn meal works.

I'll put one up on Nostr eventually, but it's going to be a while. With a couple exceptions, I try to limit recipe piracy to when I actually make something, so I at least have original (but usually awful) pictures. 😅