Question10_practical.cs

using UnityEditor;
using UnityEngine;

public class Question10_practical : EditorWindow
{
    [MenuItem("Window/Question10_practical")]
    private static void Open()
    {
        GetWindow<Question10_practical>();
    }

    private Question10_RectData_practical rectData;

    void OnEnable()
    {
        rectData = CreateInstance<Question10_RectData_practical>();
    }

    void OnGUI()
    {
        if (Event.current.commandName == "UndoRedoPerformed")
        {
            Repaint();
            Focus();
        }

        BeginWindows();

        rectData.windowRect = GUI.Window(0, rectData.windowRect, (windowID) =>
        {
            Undo.SetSnapshotTarget(rectData, "Moved Window");

            if (Event.current.type == EventType.MouseDown)
            {
                Undo.CreateSnapshot();
                Undo.RegisterSnapshot();
            }

            GUI.DragWindow();
        }, "");

        EndWindows();
    }
}

Question10_RectData_practical.cs

using UnityEngine;

public class Question10_RectData_practical : ScriptableObject
{
    public Rect windowRect = new Rect(0, 0, 100, 100);
}