Khao niao khanun isn’t nearly as popular or ubiquitous as the iconic khao niao mamuang (sticky rice with mango), but it’s by no means uncommon. And if you already know how to make the latter, you already know enough.
Start off with a fresh batch of sweet coconut sticky rice. Page 161 of Simple Thai Food explains in detail the process of making it. Then you pinch off a small bit of the rice and fill a fresh jackfruit half (you already know how to get the flesh out of a whole jackfruit) with it. The salted coconut cream goes on top. If you’re in Thailand, fried hulled mung beans would be the standard topping; elsewhere, sesame seeds would work just fine.
Once assembled, these stuffed jackfruit halves should be consumed as soon as you can. Certain things don’t taste great after having sat at room temperature for a long time (or reheated after having been refrigerated). This is one of those things.