Is vitamin c prevents sore throat testable by scientific inquiry

There is not enough evidence to support that vitamin C aid in sore throat. But there is no harm too.

In the medical field, every treatment should be supported by evidence. This practice called evidence-based medicine. There is so much drug claim that actually wasn't supported by research and might be potentially doing more harm than benefit. Theory or argument about why it should work is not enough, you need to do a research to find the truth.