class QuestionsVM
    {
        public ObservableCollection<QuestionVM> Questions { get; set; } = new ObservableCollection<QuestionVM>();

        public void AddQ()
            => Questions.Add(new QuestionVM(this));
    }

    class QuestionVM
    {
        public QuestionVM(QuestionsVM obj)
        {
            AddNewItem = new RelayCommand<object>(o => obj.AddQ());
        }

        public ICommand AddNewItem { get; set; }
    }