This quest requires you to obtain 2 Certus Quartz Crystals, which can most commonly be found from y-level-35 to y-level-47.
Keep in mind that Certus Quartz Ore is a level 1 ore, meaning it cannot be mined with Flint tools, you need to have at least Copper tools to mine Certus Quartz.
Extra Guidance[]
Upgrading your pickaxe[]
Certus Quartz Crystals cannot be melted in a smeltery, so to make a Certus Quartz Pickaxe (Which you need to mine Iron Ore) simply make a Certus Binding, Tool Rod, and Pickaxe Head, and put the 3 items in the Tool Station where you can make the pickaxe.