Snap on an iPad will speak when the buttons have actions that speak immediately. example: Quick fires,
When words are inserted into the message window and you select Speak, there is no sound output.
Snap App will not speak when I have items in the message window and I select the Speak button. It also will not speak as it is inserted in to the message window and I have the speak when inserting into the message window is on.
Buttons will speak that have the action of Message behavior: Always speak set in the Action of the button.
In the Settings of the iPad check the Silent mode. If it is off (red bell) change it to On ( white Bell)
To access the control panel on the iPad slide up from the bottom of the home screen.
If you have upgraded to iOS 12, Slide down from the top right corner, where the battery and wifi status is.