Mo learned information in her position by speaking with secretaries and clerks in informal settings, such as in the lunchroom. this is an example of what kind of message system?

This is an example of "grapevine".

Grapevine is a casual, informal and individual correspondence channel or framework that happens inside the association because of talk and chatter. It is a mind boggling web of oral data stream connecting every one of the individuals from the organization. To hear something through the grapevine is to learn of something casually and informally by methods for talk or gossip.