How can I get a quote read out loud by Siri?

You need to add Siri Shortcuts for this. Go to the app Settings and tap on 'Siri Shortcuts'. Next tap on the category you want to add Siri shortcut for. The app will ask you to set a phrase you would like to speak, just write the phrase and tap on Add to Siri. Now you can get a quote from that category read out loud by Siri by saying the same phrase.