  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.
