If you chose for the option to simulate the Witcher 2 save you will be asked some questions by an NPC right after the prologue. More specifically,

>! this happens right after you killed the griffin and decide to go to Yennefer. You meet her, she takes you with her and you meet a king, then during a shaving scene you get asked some questions about the witcher 2 decisions.

These questions are (Spoiler for Witcher 2 - Assassin of Kings):

>! - Did you kill Aryan?  
>! - Did you choose Yorveth or Roche?  
>! - If you picked Yorveth you'll 2 choices: did you save Triss or break
>!   the curse of Saskia? If you picked Roche did you save Triss or help
>!   him save Anais?  
>! - Did you help Sile in the Megascope or not?  
>! - Did you let Letho go or not?