Energy of a complex exponential
As mentioned in the comments you can just take the integral of the squared magnitude.
Notice that the magnitude of $|e^{a+bj}| = |e^a||e^{bj}| = e^a$ for $a,b \in \mathbb{R}$, comparing with your function we see that $|x_i(t)|=1$. We conclude that $x_i(t)$ is a power signal, not an energy signal, i.e. you must define a time interval to integrate. Then the energy will be $\int_{t_0}^{t_f} |x_i(t)|^2  \mathrm{d}t = (t_f - t_0)$. I hope this helps.