We investigate the measurement of non-standard ZZV (V = {\gamma}, Z) couplings through Z-boson pair production at the e+e− colliders. We adopt Standard Model Effective Field Theory (SMEFT) approach to study these anomalous neutral triple gauge couplings. There are one CP-conserving and three CP-violating dim-8 SMEFT operators that contribute to ZZV couplings. Using optimal observable technique, the sensitivity of these NP couplings has been estimated and then we compare it with the latest experimental limits on dim-8 couplings at CERN LHC. Effect of beam polarization and correlations among CP-violating ZZV couplings are discussed. Comparison of statistical limits of new physics couplings between optimal observable technique and contemporary cut-based analysis has also been studied in detail.