I managed to sprout a nut and now I have a walnut. Can I make a bonsai?
Yes and no. Indeed you can make a short tapering trunk as with any deciduous species, but the leaves remain just about as big as one in an orchard. So it isn't very pleasing in leaf.
However, most deciduous bonsai are prized for their branch structure which is seen in winter. In my experience, it is frustratingly difficult to make a nice branch structure because of the large compound leaves.
I had a lot of fun with sprouts from seeds that were apparently planted by squirrels in my yard. I grew them in a larger pot until the seedling didn't need the nut, then planted them in very small (one or two inch diameter) pots. It found it quite amusing to have two or three inch long trunks with 6 inch compound leaves hanging off them! They are indeed a lot of fun for a while. Other species like horse chestnut and maples miniaturize themselves when kept small and are much more rewarding as legitimate bonsai.
Perhaps Google translate will help.