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 JenniferYennefer. 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?