If a Present cannot hear the audio from a video they are playing during a ScreenShare you need to check the audio settings on their computer. Below are two potential solutions.
USE HEADPHONES: Some laptops will play video audio to headphones but not the speakers when screensharing in Zoom.
CHANGE AUDIO OUTPUT SETTINGS:
For PC (Windows 10)
Go to Settings (click Windows key on their keyboard, or Windows icon - leftmost icon on taskbar)
In Settings click System
In System click Sound, then click Advanced sound options
In the Sound menu, click Advanced sound options
Try setting the PowerPoint Slide Show to Default, if that doesn't resolve the problem, try the other options available.
For more help with Zoom audio issues see: Troubleshooting Audio Issues