It's possible that it's:
* A misspelling: It might be a misspelling of a different word. Could you please provide more context about where you encountered this word?
* A slang term: It might be a slang term or regional dialect word. If you can tell me where you heard it, I might be able to help.
* A word from another language: If you can provide the language it comes from, I can try to find its meaning.
Please give me more information so I can help you understand what "bonjia" might mean.