What is the ruling on academic discussion between two or more people during the circumambulation (Tawaf) or the ritual walk (Sa'i)?

Scholarly discussion during tawaf and sa'i does not invalidate them, but it is better to engage in dhikr (remembrance of Allah). As for a quick answer to an incidental question, there is no harm in it as long as the questioners are not numerous. It is permissible for the one being asked to request the questioner to wait until he finishes tawaf to dedicate himself to dhikr.