Answer
\begin{align*}f'(x)&=e^x e^{e^x} .
\end{align*}
Work Step by Step
Recall that $(e^x)'=e^x$
Since we have
$$ f(x)= e^{e^x}$$
then the derivative $ f'(x)$, using the chain rule, is given by
\begin{align*}f'(x)&=e^{e^x} (e^x)'\\
&=e^x e^{e^x} .
\end{align*}