How can I calculate the Cimon in a DC-DC converter?
The answer is in the datasheet, at page 10.

\begin{equation}
C_{IMON}R_{IMON} \geq \frac{1.59}{f_{SW}}
\end{equation}

Using your values,

\begin{equation}
(10 \text{ nF})(10 \text{ k}\Omega) \geq \frac{1.59}{f_{SW}} \Rightarrow f_{SW} \geq 15.9 \text{ kHz}
\end{equation}

The switching frequency is set by \$R_T\$ as described at page 11.

\begin{equation}
f_{SW} = \frac{10^5}{R_T \text{ (k}\Omega)} \Rightarrow R_T &lt; 6.289\text{ k}\Omega
\end{equation}