Resourceful

For anyone doing legacy achievements, and needing this one, engineering is by far the easiest profession for it. All rank 2 recipes can be purchased for gold. No reputations required. No hidden recipes to farm. I did it in a matter of minutes once I completed the primary engineering quest chain.

Mouse over and click the star in the recipe and it will tell you where to get the next level. This is true for all professions. Just to clarify, open the recipe, mouse over and click the stars and you get a popup. At the bottom of that popup it tells you where to get the next rank. Hope that helps

A little more detail: it's Legion Engineering you want. At the time of writing the achievement will pop if you do this requirement just for Legion; you don't have to mess with BFA or shadowlands. You want to do the quest chain from the engineering NPCs in dalaran *all the way through the Court of Stars dungeon quest*. After that, you can stop. Then, buy all rank2s you can find from NPCs in the dalaran engineering building, and also from Fargo Flintlocke in Aszuna. If you are having any trouble, in your professions window you can see unlearned recipes and location of rank2 recipes.