It's more of the soft G/J sound, like Djorou. Phonetically I suppose the correct denotation is Zhaka. Fairly certain it's not the hard "ch" as in chalk.
It's Serbian, similar to Shaquiri's first name, which is anglicized Xherdan, but pronounced more like "Jerdan". I think Jones touched on it on this thread so he probably knows more than I do about it