hi!
the problem in your code snippet was, that dy is an int not a var (open the NativeFONT.cs to see what type a variable has)! This snippet should work.
Code:
/// <summary>
        /// dy - see Gamestudio manual
        /// </summary>
        public int dy
        {
            get
            {
                unsafe
                {
                    return (*FONTPointer).dy;
                }
            }
        }

Maybe I will include some unlisted properties of engine objects in the next release (which I will release, when the new engine version isn't in public beta anymore)