In the books
In the A Song of Ice and Fire novels the House of Qaggaz is one of the most powerful families of Yunkai. The known members of the family are Yezzan zo Qaggaz and his four nephews, and his heirs, one of which is killed by either the Second Sons or the Stormcrows when the Yunkish forces march on Meereen.
In the novels Yezzan was from Yunkai, but in Season 5 he only appeared at Meereen to buy slaves to use in the gladiator games - but so does Yezzan in the novels, and thus he could be a Yunkish slaver simply visiting Meereen. Subsequently in Season 6, however, Yezzan returned to represent Astapor at the diplomatic negotiations. At the least, this casts doubt that he should automatically be assumed to be from Meereen. Given that Yunkai reconquered Astapor and reconstituted the slave-masters there, it's plausible that he is still a Yunkish slave-master, simply appointed to oversee the re-establishment of the other slavers in Meereen. Exactly which of the three major cities of Slaver's Bay TV-Yezzan is supposed to be from is therefore unclear. Then again, he doesn't necessarily need to be "from" one of them, as there are slave-masters and merchants that move around between the slave-markets of all three cities to conduct trade.