Answer
$H^+$: Lewis acid
$N{H_2}^-$: Lewis base
Work Step by Step
The $N{H_2}^-$ has one pair of electrons free, so when it reacts with $HIO$, the $H^+$ will receive that pair.
Since $N{H_2}^-$ donates one pair of electrons, it is the Lewis base.
Since $H^+$ receive these electrons, it is the Lewis acid.
