$(1)$ $\begin{matrix}
C{{H}_{3}} \\
|\,\,\,\,\,\, \\
ZNH\,C\,HC{{O}_{2}}H \\
\end{matrix}$ $(2)$ $\begin{matrix}
C{{H}_{3}}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, \\
|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, \\
{{H}_{2}}N\,C\,HC{{O}_{2}}C{{H}_{2}}{{C}_{6}}{{H}_{5}} \\
\end{matrix}$
$(3)$ $\begin{matrix}
\,\,\,\,\,\,\,\,\,\,\,\,C{{H}_{3}}{{C}_{6}}{{H}_{5}} \\
|\,\,\,\,\, \\
ZNH\,C\,HC{{O}_{2}}H \\
\end{matrix}$ $(4)$ $\begin{matrix}
C{{H}_{2}}{{C}_{6}}{{H}_{5}}\,\,\,\,\, \\
|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, \\
{{H}_{2}}N\,CHC{{O}_{2}}C{{H}_{2}}{{C}_{6}}{{H}_{5}} \\
\end{matrix}$
If the absolute values of the net charge of the peptide at $pH =2, pH =6$, and $pH =11$ are $\left| z _1\right|,\left| z _2\right|$ and $\left|z_3\right|$, respectively, then what is $\left|z_1\right|+\left|z_2\right|+\left|z_3\right|$ ?