Is the unit for equilibrium constant for reaction 2H₂O → H₃O⁺ + OH⁻?

The question seems to be incomplete. Assuming you are asking for the unit of the ion-product constant for water (\(K_{w}\)), which is the equilibrium constant for the autoionization of water (\(2H_{2}O\rightleftharpoons H_{3}O^{+}+OH^{-}\)), the unit is \(mol^{2}\cdot L^{-2}\). This is calculated from the concentration units (mol/L) of the products, \(H_{3}O^{+}\) and \(OH^{-}\). The concentration of the solvent, water, is considered constant and is not included in the expression for \(K_{w}\).