Ciri is the daughter of Emhyr var Emreis, emperor of Nilfgaard, and of Pavetta, heiress to the throne of Cintra. She was raised by Geralt as an adoptive daughter of sort and trained in Kaer Morhen (although she was never submitted to the full witcher mutations). Yennefer also helped raising her, and so did Triss, Vesemir, Eskel and Lambert. All this is narrated in detail in Sapkowski's book saga.