public class CursorSceneCoordinates : EditorWindow
{
  private Vector2 _scenePosition;

  [MenuItem("Cursor Scene Coordinates")]
  static void Init()
  {  
  CursorSceneCoordinates window = GetWindow<CursorSceneCoordinates>();
  window.Show();
  }

  private void OnEnable() { SceneView.duringSceneGui += SceneViewDuring; }  

  private void OnDisable() { SceneView.duringSceneGui -= SceneViewDuring; }

  private void SceneViewDuring(SceneView scene)
  {
  var e = Event.current;
  if (e.type == EventType.KeyDown && e.keyCode == KeyCode.Space)
  {
  float pixelsPerPoint = EditorGUIUtility.pixelsPerPoint;
  Vector2 mouse = e.mousePosition;
  mouse.x *= pixelsPerPoint;
  mouse.y = scene.camera.pixelHeight - mouse.y * pixelsPerPoint;
  _scenePosition = scene.camera.ScreenToWorldPoint(mouse);

  Repaint();
  }
  }

  void OnGUI()
  {
  EditorGUILayout.LabelField("Scene: ", _scenePosition.ToString());
  }  
}