Suffered facial palsy post craniotomy. face appears mostly normal but when i smile or laugh my lip twitches. is this synkinesis or nerve irritated?

Probably weakness: There's no way to know without seeing it but usually synkinesis is the yoking of the movements of the eye and mouth: when you smile you blink and vice versa but only on the damaged side. Twitching of a previously damaged area is likely residual weakness from the injury or continued irritation. Would be tough to get isolated lip irritation from a craniotomy injury. I would go with weakness