I don't recall any 121 reg questions so I wouldn't waste much time. It was literally read this metar, what are these symbols on an enroute chart (she just randomly pointed to various symbols on an enroute chart), what can you tell me about this airport on the enroute chart, brief this approach (yes, a big scary mexican approach chart which is identical to every Jepp plate you've ever read ). Next room, tell me about X system on the twin you are most familiar with. I was asked about the engines, other people were asked fuel system, electrical system, etc. Final room is HR. Usually someone from the training department is there, he will try to throw you off balance but just don't get flustered. Then the standard incidents, accidents, training difficulty, failed checkride questions. No sweat. Might have changed some, its been almost a year since i interviewed.