Ninassa is mentioned in the tablets of the Kanesh merchants, and also in the archives of Hattusa.
Concerning its location, in the Palaeo-Assyrian archives, it appears that the city was close to an important river, since several tablets (including kt94 / k1534 which evoke a travel from Washaniya to Nenassa) mention the payment of a bridge keeper.
Here are the main references in the Hittite archives:
King Labarna Ist had installed his son to Ninasa and Hupisna, near Ussa;
In the annals of Hattusili I, in a campaign against the Arzawa, Ninassa opened its doors without a fight;
In the Edict of Telepinus "At Hupisna, at Tawanuwa, Nenassa, Landa, Zallara, Parsuhanta, Lusna; those countries, the Tabarna governed them and the great cities were placed in his grasp."
Ammuna was Prince of Sukziya, of Pimpirit and of Ninasa.
In the Alalakh tablets, the city is probably called Naazizi.
Nenizi - Bekarlar near Nevsehir, has been identified as the ancient Nanassos or the Byzantine Nazianze by inscriptions found on two tells of the city. This town was known as a place of birth of Gregorius Nazianzenus, or Saint Gregory of Nazianzen, the 4th century AD theologian :
Other researchers have positioned Ninassa 10 km southwest of Aksaray, to the city of Mamasun, which would be the ancient Byzantine Momasum. The latter hypothesis is supported neither by archaeological evidence, nor a phonetic approximation between the Hittite name and the Greco-Roman name.
My notes of veracity :
Ninasa, Ninassa or Nenassa was the city of Nanassos or Nenizi, near Nevsehir: 3/5
Ninasa, Ninassa or Nenassa was Mamasun near the city of Aksaray: 1/5