Like Tieliebirds said, the jya rhymes with 'spa', and is one syllable. When looking at Italian gi- words it's easiest to forget the 'i' and pretend that the 'g' is a 'j'. For example,
Giulia is pronounced exactly the same as
Julia.
Gianina - ja-NEE-na - rhymes with
MarinaGianna - JAN-ah - rhymes with
HannahGiovanna - jo-VANNA - doesn't rhyme with anything!
Italian vowels are *very* specific - each vowel letter represents only one sound in most cases, unlike in English where vowels are all over the place. In this case, it's 'a' as in "cat", 'i' as in the 'ee' in "free" and 'o' as in "joke".