When Capturing City-States do bonuses remain?
Once you capture a City-State, it is no longer a City-State, and you do not receive the bonuses due to being a City-State's ally. So that bonus Faith, Culture, Food, etc. disappears entirely, and Porcelain and Jewelry also disappears. Only Mercantile City-States produce Porcelain or Jewelry, so it's treated like any other City-State bonus and it goes away.
Once it's your city, it acts just like any other city you've captured, and it does not have any special bonuses.