If you chose for the option to simulate the witcher 2 save you will be asked right after the prologue some questions by an NPC.
Care: The Witcher 3 - Wild Hunt spoilers ahead
This happens right after you killed the griffin and decide to go to Jennifer. 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.
Care: The Witcher 2 - Assassin of Kings Spoilers ahead
These questions are about:
- killed or spared Aryan LaValette
- sided with Iorveth or Roche
- saved Triss or saved Saskia/Anais
- saved Sile de Tancarville or let her die
- killed or spared Letho