Hi, I'd like to help you with your question.
As long as you have no reason to doubt your wife's word (she hasn't lied or cheated in the past), there should be no reason to be concerned. That does not mean you can't feel upset about it or a little jealous and let her know you feel that way. But asking her to give up seeing this man in a class may be a little too much to ask. If the co worker was just keeping her company and they both stayed in open, public areas then there is probably nothing going on.
However, if your wife starts to make a habit of seeing this co worker, especially over seeing her female co workers, or she starts to go out of her way to see him in other circumstances and tries to keep it secret, then you have a right to ask her to stop. Married people should not be close friends with the opposite sex without the involvement of their spouses. Boundaries are easy to cross in that case.
Trust is important in a marriage so as long as you have no reason not to trust your wife, allow her to use her best judgment on this situation.
I hope this has helped you,Kate