Input capacitance, Ci, is measured between the input terminals with either input grounded. Ci is usually on the order of a few pF. To relate Ci to Figure 5-6, if you ground Vp, Ci = Cd || Cn.
Sometimes common-mode input capacitance, Cic, is specified. To relate Cic to Figure 5-6, if you short Vp to Vn, Cic = Cp || Cn, the input capacitance a common mode source would see to ground.