He’s a good bit like his father in how he enjoys gardening, for one, although Asriel loves all kinds of plants and eagerly strays away from just the golden flowers. Wildflowers, roses, lilies, tulips, all of them are cool! Another big hobby of his is dancing: he’s very into waltz and ballet, and wants to learn more popular forms of ballroom dancing. Cooking is something he’s pretty good at and could consider getting into, but it’s not as big a thing as the other two. Also, romping through the woods with Chara (and maybe Frisk too)! He loves nature and animals and all sorts of stuff you can find out there, he’d probably bring home all the injured animals ever.
Other stuff includes general interest in politics and fancy things like history, written language and philosophy. He wants to grow up to be a good ruler, so he has to know all about the world and its history and people.