。
Nobody knows what will happen tomorrow.
Literal
Tomorrow what [subject-が] happen [question-のか] [topic-は] nobody [to-に] know-not.
Uses 起きる instead of 起こる for 'happen' — both are valid and overlap heavily, with 起きる being slightly more colloquial and 起こる leaning slightly more written. The のか adds a slightly more emphatic or emotional coloring to the embedded question. The combined sense of 'nobody truly knows what tomorrow holds' is a recurring aphorism in Japanese speech.