How long before you can 3D print Explosives inside an item ?
It probably can be done today...
I think it could be done, but I do not see much utility to it.
There are 3D printers that can print in multple materials. Just have them print the outside if the item in two materials: Epoxy and hardener, and the inside in plastic explosive.
But, you could get the same effect by creating an item with a void, and then injecting the explosive into the void and sealing up the hole.