You can do hit detection using the SkeletonBounds class, which gives you access to the bounding box attachment polygons (you can also access the polygons directly from the attachments, but SkeletonBounds collects them for you). The polygon coordinates are specified in "world" coordinates, which for Unity is relative to the SkeletonAnimation gameobject. You can transform these as needed, depending on what other gameobject you need to do hit detection with.
Ideally the Unity Spine runtime would use colliders to do hit detection, but this has not been implemented yet. Rob has been working on this, as he mentioned. BTW, welcome back Rob! 😃 I had wondered where you'd gone to!