im making a simple pong clone in unity using the 2d tools provided. I have it up and running with the ball x velocity switching when it hits a player, and the y velocity switching when it hits a wall:

void OnCollisionEnter2D(Collision2D collision) {
        // Invert the velocity
        if (collision.gameObject.name == "Player")
        {
            if (speed > 0)
            {
                speed++;
            }
            else
            {
                speed--;
            }
            speed = speed  * -1;
         rigidbody2D.velocity = new Vector2 (speed, UpDown);
            print ("i hit player");
        }

theres a couple of extra lines in there, which increase the ball speed on every hit and also print a debug message onto the console. Any tips on modifying it so that the area of the player paddle that is hit will affect the UpDown(y axis) of the ball?

I'm guessing that you collision.gameObject is the full object of the Player and that rigidBody2D is the ball, if not I guess you can get a pointer to those objects some how.

With the Y position of the ball and the Y position of the Player and the height of the Player you can see how far is the ball to one of the ends of the Player.

With those values you can make a linear function that returns an angle between [-a , a], and with functions like acos and asin of that angle you can get how much to increment the x and y speed. You can test for different "a" angles to see which value makes more sense (maybe 45 degrees?).