public static void Main()
    {
        B i=new B();
        MemberInfo[] mis = i.GetType().GetMembers();
        if (mis.FirstOrDefault(c => c.Name == "a") != null)
        {
            MemberInfo mi = mis.FirstOrDefault(c => c.Name == "a");

            // Now I want to access member of a via mi
        }
    }

    public class A
    {
        public int i { get; set; }
        public void test() { }
    }

    public class B
    {
        public A a { get; set; }
        public B()
        {
            a = new A();
        }
    }