My husband is the beneficiary and the questions asked were pretty easy he said like, how we met, how long we've known each other -- just simple personal questions really
The 221g was for the AOS, actually during the interview they requested for the end of 2013 paystubs, and he only had the December copy with him and they wanted more thus the 221g, plus on the email we received regarding the 221g instructions when he got home they wanted me to submit an updated AOS i864 as well as an i864a from my mom, which was weird since during the NVC period i only submitted an i864EZ form coz my current salary have met the poverty guidelines anyway... but regardless we just complied and submitted whatever they need and got the visa issued after 11 days from his interview
If you have your interview set, just prepare all the documents needed and also provide updated copies of those like 2013 W2, ITR (if available) and paystubs just to be safe.. hope this helps and goodluck!