The major problem with interview cases is that sometimes it takes a long time to get an appointment. In San Jose, it's not that bad, about 1,5 months. However, SFO is screwed.
In the interview notice, they'll tell him what he needs to carry - probably the originals of all filed documents as well as evidence that marriage is still "bonafide" and employment verification letter.
The questions are general, usually to establish that the company is legal, not fictitious, then about marriage and that's mostly it. After these, the IIO goes through all paperwork, asks for original birt certificate, original marriage certificate (with translations), looks if FBI anf background check went well. Then she looks at medicals and if everything seems OK, she stamps the passport.
Sometimes they sent applicants to interviews for a reason, in which case your friend would get to know it if not in the interview notice then in person.
