Consider this equilibrium: i2(s) + h2o(l) h + (aq) + i-(aq) + hoi(aq). what is the keq expression for this equilibrium?

The equilibrium expression relates the concentrations of the products to the concentrations of the reactants, for the species in solution, this means that it does not use the liquids or solid substances => Keq = [H+] [I-][HOI]. As said, I2 (solid) and H2) (liquid) do not appear in the expression, because as solid and liquids their concentrations do not change.