It's a phrase that expresses concern or curiosity about someone's future. It can be used in a variety of contexts, such as:
* Asking about a friend's future plans: "Qué será de ti después de graduarte?" (What will become of you after you graduate?)
* Expressing worry about someone's current situation: "Qué será de ti si no consigues trabajo?" (What will become of you if you don't get a job?)
* Reflecting on a person's past and present: "Qué será de ti, mi querido amigo?" (What will become of you, my dear friend?)
The exact nuance of the phrase can vary depending on the context and the speaker's tone of voice.