The SkeletonGhost is not a shader but a component available in the spine-unity runtime. It is still available and can be found in the Spine Examples directory. You might have missed installing the Spine Examples directory from the unitypackage or UPM package. You can find the SkeletonGhost component in the following location: https://github.com/EsotericSoftware/spine-runtimes/tree/4.2/spine-unity/Assets/Spine%20Examples/Scripts/Sample%20Components/Ghost.