What drill should I work on to hit down on the ball and get ball turf?
You don't ever have to "hit down" on the ball to trap it. Trapping and Compressing the ball happens automatically as a side effect of a correct swing. If you're not compressing the ball through impact, you're doing something wrong. It might be setup, but usually the culprit is "flipping".
The ball is hit down upon automatically, when the shaft leads the club face through impact. We create this action because we use the body to "drag" the arms/club through impact, around to the left (right hander). The body's rotation keeps the shaft ahead of the club face as long as the "hands" don't take over and flip.