I wanted to ask how I get iron gold and diamonds on a normal vanilla skyblock version 1.12.2
Well, as far as I know you can get iron by killing zombies and iron golems and nuggets by killing zombie pigmans.
Normally you play Skyblock with plugins or mod to get different items.
I do not think so. Possibly. Dropped zombies iron, but not enough. I do not know how it should work otherwise.
Iron: Iron Golem Farm and Zombies
Gold: Zombie Pigman Farm in the Nether
Diamond Tools: Villager
Diamond Armor: Villager, Skeletons, Zombies