کجایی؟ (Koja-yi?)
This is a casual and informal way to ask someone where they are.
Here are some other options, depending on the context and formality:
* کجا هستید؟ (Koja hastid?) - Formal, used for showing respect or addressing someone older or in a position of authority.
* کجا هستی؟ (Koja hasti?) - Slightly more formal than "کجایی؟"
* تو کجایی؟ (To koja-yi?) - More casual, used with friends or close acquaintances.
The choice of which phrase to use depends on your relationship with the person you're asking.