There may be a problem with the headphone jack or with the internal speakers.
Depending on the type of headphone jack, there can be an internal contact that is operated when you plug in a headset that “tells” the audio controller to switch the audio away from the internal speakers to the headset connection. Alternatively, the headphone socket may have contacts that “break” the audio path to the internal speakers and allow the audio to connect to the headphones when a headset is inserted.
It could also be that the internal speakers are faulty or have a faulty connection.
In either case the tablet needs to be opened and the problem further investigated.
Here’s a link to the ifixit Trio Stealth G2 Hype Speakers Replacement guide, which may be of some help.