PatchExtensions.cs

 public static class PatchExtensions
    {
        public static bool HasBeenChanged<T, TProperty>(this JsonPatchDocument<T> patch, Expression<Func<T, TProperty>> field) where T : class
        {
            var fieldPathWithPrefix = field.Body.ToString().Replace(".", "/");
            var fieldPath = fieldPathWithPrefix.Substring(fieldPathWithPrefix.IndexOf("/", StringComparison.InvariantCulture));
            return patch.Operations.Any(x => x.path == fieldPath);
        }
    }