using System;

using System.ComponentModel;

public class Program

{

    public static void Main()

    {

        var parent = new ViewModel();

        var child = new SubViewModel(parent);

        child.PropertyChanged += (sender, e) => Console.WriteLine($"{sender}.{e.PropertyName} has been updated.");

        parent.Property = "test";

    }

}

​

    public class SubViewModel : INotifyPropertyChanged

    {

        private ViewModel parent;

        public event PropertyChangedEventHandler PropertyChanged;

        public SubViewModel(ViewModel parent)

        {

            this.parent = parent;

            this.parent.PropertyChanged += (sender, e) => PropertyChanged?.Invoke(this, new PropertyChangedEventArgs("SubProperty"));

        }

        public string SubProperty

        {

            get { return parent.Property; }

        }

    }

    public class ViewModel : INotifyPropertyChanged

    {

        public event PropertyChangedEventHandler PropertyChanged;

        private string property;

        public string Property

        {

            get { return this.property; }

            set

            {

                this.property = value;

                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs("Property"));

            }

        }

    }