The word “reasonably” means that the public office holder made an effort to find out whether a given situation would put them in a conflict of interest. That may involve the public office holder asking Mr. Dion, the Conflict of Interest and Ethics Commissioner, whether taking part in a given discussion would put them in a conflict of interest.
It might also involve the public office holder seeking legal advice or asking their superior, depending on their level. Being reasonable means thinking to get the information. The person might tell the public office holder that they will get back to them in two weeks, but the public office holder may have no choice but to attend the meeting in an hour. That is what “reasonable” means, in my view. The person has to be quick-witted enough to ask the question.