Typically even in an informal interview I will have reviewed a candidate's resume. So yes, to some degree, I will have learned about the candidate's occupation. The purpose of the interview will then determine how much detail I go into with the candidate on their occupation. Is it the first step toward employment for an open job for which the candidate is qualified? Is it a courtesy interview where I'm helping a candidate learn about a company? Am I simply helping a student to polish their interview skills? The level of formality and explorations of one's occupation and related qualifications can change significantly based on the answer to many of these questions.