Sunya is a Farsi/Turkish name meaning "light of her grandparents", it comes from Su ("light" in Pahlavi) and Nya (grandparents in Pahlavi). It means a girl who is the joy and happiness of her grandparents. It is not a Quranic/Islamic name but since the meaning is good Muslims can use it. It is pronounced as (S)weet + p(U)t + (N)ame + (YA)rn.
Sunya can also be another spelling of Sonya, which is the Russian version of Greek Sophia, which means wisdom.
You may also be interested in the name Saniyya: Sanniya