Where to Find Kenneth Haight
From the Mistwood Outskirts, head in a northeasterly direction until you come to a large ruin that is falling apart and creating a partial bridge. You will be able to hear someone asking if you would like to assist the great Kenneth Haight as you get closer to the location. As you make your way to the top, be careful not to let any enemies follow you there; if they do, Kenneth Haight’s storyline will end much sooner than it should. It is important to take note, however, that when he passes away, he leaves behind a Golden Seed.
After you have a conversation with him, he will ask you to return his ancestral fort, which is Fort Haight. To move forward with his mission, you will need to agree to be his servant and pledge your support to him (this will not lock you out of any other NPC questlines or have any impact on storylines). Make a solemn oath to him to serve him, and then travel to the extreme southeastern corner of the eastern Limgrave region to locate Fort Haight.
After you have defeated all of the foes inside the Fort, you will need to reload the area to find Kenneth Haight waiting for you near the top of the Fort. He will tell you that he has to find a new Lord to take the place of Godrick the Grafted, and then he will retract his offer to make you a knight in the order. After yet another round of reloading the area, you will find that he has moved to his permanent position within Stormveil Castle.
At Stormveil Castle
In order for Kenneth Haight to show up in his permanent location, the following prerequisites need to be satisfied:
After meeting the requirements listed above, Kenneth Haight and Nephali Loux can be found together in the throne room of Stormveil Castle (just beyond the Godrick, the Grafted Site of Grace).
Talking to Kenneth Haight will make it clear that he has selected Lady Nepheli as the new ruler of the realm. Nepheli will express her gratitude for your assistance if you talk to her; if you continue the conversation, you will be rewarded with an Ancient Dragon Smithing Stone. She promises that if you become the Lord of Elden, she will make things easier for you.
By moving Kenneth Haight and Nepheli Loux to the throne room in Stormveil Castle, you will be able to interact with Gatekeeper Gostoc and gain access to his shop. In his shop, you can buy an Ancient Dragon Smithing Stone for 20,000 Runes.