Rule reminder
Left dislocation is frequently used to establish a contrast between two elements: 'Questo film, l'ho visto. Quell'altro, no.' The second element is often left-dislocated without a full predicate (ellipsis), relying on the contrastive structure to convey meaning. This is a hallmark of Italian conversational syntax.
What is the rhetorical function of 'Questo l'ho capito. Quello, invece, non ci ho capito niente'?