We present the results of optical spectroscopy for 58 quasar candidates at photometric redshifts z>~3, 57 of which enter into the Khorunzhev et al. (2016, Cat. J/PAZh/42/313) catalog (K16). This is a catalog of quasar candidates and known type 1 quasars selected among the X-ray sources of the 3XMM-DR4 catalog of the XMM-Newton serendipitous survey. At first we have performed spectroscopy for a quasi-random sample of 19 candidates at the 1.6-m AZT-33IK telescope of the Sayan Solar Observatory and the 6-m BTA telescope of the Special Astrophysical Observatory (SAO RAS). Then we have continued the observation for 39 X-ray bright candidates that could be used for the X-ray luminosity function construction (see Khorunzhev et al. 2018AstL...44..500K). The spectra at AZT-33IK were taken with the new low- and medium-resolution ADAM spectrograph that was produced and installed on the telescope in 2015. One of the most distant (z=5.08) optically bright (i=21) quasars ever detected in X-ray surveys has been discovered.