For vertical center...it has already been pointed out that you can find that where the ball touches the cloth.....
For Horizontal center. On any table that has overhead lights....you can see a lighted portion of the ball and a shaded portion of the ball (below horizontal center)....horizontal center is the transition point between light and dark......(most people just don't pay attention that it is there)
However....it is very rare to shoot exactly horizontal center.........for a stop shot...most times you are hitting about 1/4 or 1/2 tip below center....or.....just barely into the shaded area.....for draw you are hitting further into the shaded area.......for follow......you shoot into the lighted area
Unless of course you are jacked up....you may shoot into the lighted area for draw since the CB axis changes....but you can still use the lighted/shaded area as a guide on where you intend to hit.