I'd like to add loot from electroblob's wizardry and its addons in the chests under the apothosis's spawners but I don't know how to do that, so, How do I do that?.

You would need to use a datapack to override the existing loot table, and introduce the new entries that you want within it.

To receive a json-copy of the loot table, use the /placebo serialize_loot_table command for the specific table.