Yes, you need to know the FAR/AIM, but the good news is you can learn all of it over a weekend, just dive in. Think about where your interviewing - what regs do they operate by? Sure you may not have flown under those regs, but are you asking for a permanent exemption? If your not going to learn them now, then when?

Most airline ground schools are structured around students knowing and even having experience in the FAR 121 operations. As mentioned, you may be able to get away with a "don't have experience there" type answer but don't expect to get away with simply not knowing.

Experience vs. knowledge is a subtle nuance, but not one that escapes the interview board. Said another way: Go learn the regs - they are not that difficult to learn but they do come up in an interview.