  Measuring the small primordial nonGaussianity (PNG) predicted by cosmic
inflation theories may help diagnose them. The detectability of PNG by its
imprint on the 21cm power spectrum from the epoch of reionization is reassessed
here in terms of $f_{NL}$, the local nonlinearity parameter. We find that an
optimum, multi-frequency observation by SKA can achieve $\Delta f_{NL} \sim 3$
(comparable to recent Planck CMB limits), while a cosmic-variance-limited array
of this size like Omniscope can even detect $\Delta f_{NL} \sim 0.2$. This
substantially revises the methods and results of previous work.
