Does Enervation make enemies lose their spells in Neverwinter Nights 2?

Level draining effects such as that of Enervation lower the target's effective Caster Level, the calculation of which depends on character class, multiclassing, abilities etc.

the highest spell level that a character has access to depends on class, feats such as Practiced Spellcaster and prestige classes the character might have.

All in all, Enervation does effectively decrease the target's highest spell level, but it considers 'caster level' in the calculation.

Another thing to mention that, if the caster levels drained drop the level to 0 or below, the target is killed instantly. See ability drain on nwnwiki.