What does it mean if only one of your wisdom tooth aches after you eat something sweet such as trail mix and yoplait yogurt?

Caries. It may mean that you may have caries (decay) in that tooth. Wisdom teeth are known to decay quicker than other teeth because they are harder to get while brushing. I'd go to the dentist to get it checked out.
Probably decay. Without an exam it is impossible to say, but my guess is that you have a wisdom tooth with decay in it. Go see a dentost and have it checked.
Dental caries. Of course, we cannot diagnosis from symptoms alone, but it is irrelevent whether it's coming from a wisdom tooth or not. Please seek a dentist for an exam.