The electric field at the center of a uniformly charged circular ring is zero because the fields due to diametrically opposite elements cancel each other out. This implies that the electric field produced by any segment of the ring (AKB) must be equal in magnitude and opposite in direction to the electric field produced by the remaining part of the ring (ACDB) to result in a net zero field.

Mathematically, $\vec{E}_{total} = \vec{E}_{AKB} + \vec{E}_{ACDB} = 0$, which implies $\vec{E}_{ACDB} = -\vec{E}_{AKB}$.

Given that the field due to AKB is $E$. Since the charge is positive, the field direction due to segment AKB is directed away from the segment, i.e., from K towards center O (along KO). To cancel this, the field due to the rest of the ring (ACDB) must have the same magnitude $E$ but point in the opposite direction, i.e., from center O towards K (along OK).