To get the recipe you must start a chain of missions in Maldan involving a man illegally excavating ark stones in a cave. The second part of the chain is in Arborun, and you will get the Gremknight recipe by defeating him again.
( this chain is also how you get the barricadus recipe)
Tell me if this helped because i spent a while figuring this out and i want to know if other people had the same problem 