"Holding" is a term that is usually used for mouthbrooding species', but Jewels don't hold eggs/fry in their mouths.
If eggs were present and disappeared overnight then either the fry have hatched and possibly parents have moved them to a pit (usually they dig several prior to spawning), or the eggs have been eaten either by the parents or other fish in the tank, though it's unlikely Jewels would let any other fish get close if the eggs were fertile.
How long were the eggs there before they vanished? Were they fertile? If the eggs vanished within 24 hours then they have been eaten.
Mouthbrooding is most common in East African lake cichlids from Lake Malawi and to a lesser extent Lake Tanganyika. There are a few South American mouthbrooders, mostly amongst the Geophagus and Gymnogeophagus species' plus the true mouthbrooding Severum, Heros severus.