To create skin presets using ScriptableObjects and the [SpineSkin] attribute, you need to reference the SkeletonDataAsset in your ScriptableObject. Here’s a step-by-step guide on how to achieve this:

1. Create a ScriptableObject Class:
   Define a ScriptableObject class that holds a reference to the SkeletonDataAsset and the skin name.

      using UnityEngine;
      using Spine.Unity;
   
      [CreateAssetMenu(fileName = "SkinPreset", menuName = "Spine/SkinPreset")]
      public class SkinPreset : ScriptableObject
      {
          public SkeletonDataAsset skeletonDataAsset;
          [SpineSkin(dataField: "skeletonDataAsset")]
          public string skinName;
      }

2. Create Skin Presets:
   Create instances of the SkinPreset ScriptableObject in the Unity Editor. Assign the SkeletonDataAsset and select the desired skin using the [SpineSkin] attribute.

3. Apply Skin Presets at Runtime:
   Use the SkinPreset instances to set the skin on your skeleton at runtime.

      using UnityEngine;
      using Spine.Unity;
   
      public class ApplySkinPreset : MonoBehaviour
      {
          public SkeletonAnimation skeletonAnimation;
          public SkinPreset skinPreset;
   
          void Start()
          {
              ApplySkin();
          }
   
          void ApplySkin()
          {
              if (skeletonAnimation == null || skinPreset == null) return;
   
              var skeleton = skeletonAnimation.Skeleton;
              var skin = skinPreset.skeletonDataAsset.GetSkeletonData(true).FindSkin(skinPreset.skinName);
              if (skin != null)
              {
                  skeleton.SetSkin(skin);
                  skeleton.SetSlotsToSetupPose();
                  skeletonAnimation.AnimationState.Apply(skeleton);
              }
          }
      }

This approach allows you to create and manage skin presets using ScriptableObjects while leveraging the [SpineSkin] attribute to select skins conveniently in the Unity Editor.

dreding Is thre any workaround or another way to use [SpineSkin] attribute in SO? Thanks!

The [SpineSkin] attribute requires a SkeletonDataAsset to populate the popup menu accordingly with suitable skin names. If you want to avoid storing a reference to SkeletonDataAsset, you would have to omit [SpineSkin] and just use a normal string.