Answer
Conjugate Acid: $H_3C_6H_7O_5$
Conjugate Base: ${HC_6H_7O_5}^{2-}$
Work Step by Step
As we found in 16.20a and 16.20b, those are the reactions of ${H_2C_6H_7O_5}^{-}$ reacting with water as a base and as an acid, respectively:
${H_2C_6H_7O_5}^{-}(aq) + H_2O(l) -> {H_3C_6H_7O_5}^{}(aq) + OH^-(aq)$
${H_2C_6H_7O_5}^{-}(aq) + H_2O(l) -> {HC_6H_7O_5}^{2-}(aq) + H^+(aq)$