Classify the following as pi-donating, pi-accepting, or pi-non-bonding.
NH3,H2O,H2S
All are sp^3 hybrid derivatives of tetrahedral parent structure. 'pi' bonds are found in double and triple bond system... Pi bond electrons are (by 'textbook definition') the sideways overlap of unhybridized p-orbitals. So, none of the listed compounds qualify as having pi-bond electrons.
NH3 is pyrimidal with one non-bonded pair, H20 is bent with two non-bonded pair & H2S is also bent with two non-bonded pairs of electrons.
Now, if you are referring to the list as Lewis Bases in condensation reactions, then that's another story entirely. NH3 can potentially form imines =NH with nitrogen carrying pi-bonds a lone pair and one bonded pair. H2O and H2S can react with CO2 to form carbonic acid and sulfurous acid with C=O and S=O bonds that have pi-bonded electrons.