The feature to inspect recipes was added during The Burning Crusade, in 2.3.0, The Gods of Zul'Aman patch. This addon uses a database to replicate that feature in vanilla 1.12.1. Ctrl + Click a recipe, as you would any other item, to view the crafted item in the dressing room screen.

The addon's database contains all player obtainable vanilla plans, schematics, and patterns that craft an equippable item visible on the player. If you're playing on a server with custom recipes, then you'll have to add them to the RecipeDB lua. The bracketed ID is the recipe and the second ID is the crafted item.

RecipeInspect should work with the vast majority of addons. Only ones I tested that required compatibility were Atlas, AtlasLoot & AtlasQuest.