"Can you speak Chinese?"
The third one is Mandarin, which is a specific dialect of spoken Chinese. The first one is specifically oral language (Chinese). The last one is specifically written language (Chinese), however, if you are asking if someone speaks Chinese, you can use the first and last one - you'll hear people ask you that, too. 国语 is something I have never heard used, but it'd be something like the national language - it's sometimes used for Chinese like as a subject in school, and it specifically refers only to Mandarin, not other dialects.