I’m almost certain that the pull of gravity would be weakest while standing at the center of the disc. The majority of the disc’s mass is distributed to your sides, acting evenly on you in all directions, so the net downward vector would be relatively weak.

Although gravity generally acts most strongly when you’re closest to the center of mass, that would surely no longer apply if you’re surrounded by the mass. Imagine there was a hollow space at the center of the earth. You could be at earth’s center of mass and experience no net gravity, since it would be pulling evenly on you in all directions.