The code Mario gave should do what you want:
https://github.com/EsotericSoftware/spine-runtimes/blob/4.0/spine-ts/spine-webgl/tests/test-mix-and-match.html#L72-L86
var mixAndMatchSkin = new spine.Skin("custom-girl");
mixAndMatchSkin.addSkin(skeletonData.findSkin("skin-base"));
mixAndMatchSkin.addSkin(skeletonData.findSkin("nose/short"));
mixAndMatchSkin.addSkin(skeletonData.findSkin("eyelids/girly"));
mixAndMatchSkin.addSkin(skeletonData.findSkin("eyes/violet"));
mixAndMatchSkin.addSkin(skeletonData.findSkin("hair/brown"));
mixAndMatchSkin.addSkin(skeletonData.findSkin("clothes/hoodie-orange"));
mixAndMatchSkin.addSkin(skeletonData.findSkin("legs/pants-jeans"));
mixAndMatchSkin.addSkin(skeletonData.findSkin("accessories/bag"));
mixAndMatchSkin.addSkin(skeletonData.findSkin("accessories/hat-red-yellow"));
skeleton.setSkin(mixAndMatchSkin);
That is how you combine various skins into one. You can display all the skins from SkeletonData skins
, as I think you found, then combine them with code like the above.