Khaz'gorian Smithing Hammer

This achievement requires you to have crafted the Blacksmithing Tool of the Trade from BFA: [item=152839].

You must complete a quest line to obtain the pattern to craft this and have 150 skill points in Kul Tiran / Zandalari Blacksmithing.

Complete the quest line [storyline=897] (Horde) / [storyline=896] (Alliance).

Craft the item by collecting:

[item=168135] x30 - Farm [npc=137907] at 48.61, 55.39 in Silithus (BFA version).
[item=168137] x1 - Drops off [npc=134058] in [zone=9525] on any difficulty.
[item=168136] x1 - Drops from [npc=129227] in [zone=8064] on any difficulty.
Storm Silver Ore x30 - Buy off the AH.
Platinum Ore x20 - Buy off the AH.
[item=152668] x10 - You can scrap items from BFA at the scrapper in Boralus or transmute to obtain these. You cannot buy this on the AH but you can buy the items to scrap from the AH.

Titan's blood is best farmed in the MOTHERLODE dungeon

To add a bit of information to the other comment:

It appears that you now get the recipe for the Hammer after just one quest from Grix "Ironfists" Barlow / Forgemaster Zak'aal. You can then go ahead and collect all the items. However you still have to do the rest of the questline in order to obtain the Khaz'gorian Smithing Anvil required to actually craft the Hammer. The questline starts at the aforementioned Blacksmithing Trainers and ends with Anvil's Away. The anvil in front of the trainer then allows you to craft your Hammer! :)