。
I'd love to graduate next spring.
Literal
Next-year [possessive-の] spring [topic-は] graduate-want [exclamation-なあ].
なあ is an emphatic reflective sentence-final, expressing wistful longing, reflective musing, or personal emphasis — 'oh how I wish... / wouldn't it be nice...' More feelings-laden than よ or ね. 卒業したい is the desiderative on 卒業する. The whole sentence has a private-monologue feel.