Prasad's Whittaker-model expectation for distinguished representations

Let $E/F$ be a quadratic extension, let $G$ be a reductive group over $F$, and let $N_0$ be the unipotent subgroup associated with a fixed Whittaker datum. Let $\pi$ be an irreducible generic representation of $G(E)$. Prasad's Whittaker-model expectation. If $\pi$ is $G(F)$-distinguished, then $\pi$ has a Whittaker model with respect to a character

$$\psi:N_0(E)/N_0(F)\to\mathbb C^\times.$$

This is presented as an expectation concerning the Whittaker model of a distinguished generic representation, and the supplied text gives no resolution or further scope.