The first thing we've learned to always check when troubleshooting audio on the iPad is whether the device is muted or not. Go to the iPad Settings > General > Use Side Switch to: > Lock Rotation.
If you are still having issues even with the switch set to lock device rotation, try turning the physical switch to the Off position (orange hidden), restarting the app and running the kiosk presentation to see if audio plays as expected.
If that is not the issue, we recommend doing a hard reset of the iPad (holding down the Home and power buttons at the same time until the device powers down) as this has resolved issues for users in the past.
Apple's overview of how the side switch works is available here.
Note that media playback (such as music, podcasts, movies, videos, and TV shows) will play with sound in mobile Safari or some other iOS apps with the mute switch enabled (as playback is user-initiated, iOS assumes that you want to hear the audio regardless of the status of the mute switch).
We've found that, as kiosks are located in public areas, many users prefer a more consistent way of preventing sound so in Kiosk Pro these types of media will play without sound if the device is muted.
You can also set additional preferences for sound, including turning off keyboard clicks and lock sounds, under the iPad Settings > Sound.