。
Nobody knows what's going to happen tomorrow.
Literal
Tomorrow what [subject-が] occur [question-か] [emphasis-なんて] nobody [to-に] know-not [assertion-よ].
なんて adds dismissive emphasis — 'something like what will happen.' Combined with 誰にもわからない and sentence-final よ, it creates a casual, slightly philosophical assertion. The tone is 'come on, nobody can know that.'