Selection functions of high redshift quasars determined using Owl-z for Euclid I_EY_EJ_EH_E data. The selection function designs the level of completeness per redshift bin; the completeness of a bin is calculated by counting the percentage of quasars in the bin with probability is P_q > 0.1. Several cases are shown: (top panel) In red, the optical band O of Euclid is replaced by the z-band from LSST. (bottom panel) Euclid I_EY_EJ_EH_E data and in red Euclid I_EY_EJ_EH_E in addition to WISE (W1 and W2 bands).