Can Laquatus's Creativity cause an opponent to discard their hand if you have Narset, Parter of Veils on the battlefield?
Yes, but not quite. That's because Narset, Parter of Veils only stops cards drawn beyond the first, and Laquatus's Creativity is a sorcery. That means that if you cast it during your turn, opponent gets to draw at least one card (they don't have a draw step during your turn), and they will end up with one card left afterwards.


If opponent currently has no cards in hand, then Laquatus's Creativity does nothing.
If opponent has one card in hand, then they draw one and discard one.
If opponent has two cards in hand, they draw one and discard two.
If opponent has three cards in hand, they draw one and discard three.


Et cetera.

If you manage to cast Laquatus's Creativity at instant speed, then if you cast it during your opponent's turn (after their draw step when they have already drawn a card), they will indeed have to discard everything.