The Dragon Scale is a component added by Quark.
When an Ender Dragon is killed, one Dragon Scale will be dropped. This will only happen on summoned dragons by use of an End Crystal on each side of the dragon nest. You won't get one from the naturally spawned dragon. This is a 100% drop chance each time you defeat the dragon.
There is no crafting recipe.
It can be used to clone an Elytra. The cloned elytra will be dyed black, but can still be dyed again to another color.