The Legendary Necklace of Brokkr is an item that legendary blacksmith Brokkr has been longing for.
To obtain this item, you will have to find a similar-named etc-type item from corpses in Vanadis Dungeon [Lv:1] "Brokkr's Necklace" (25938). Afterward, submit the item to the Old Woman in Vanadis who will examine it and return to you Legendary Necklace of Brokkr (25409) instead.
Access to the dungeon be granted by the Chief in Vanadis. When you enter the dungeon, you will find Corpse NPCs scattered around the place. Talk to each one several times until you receive an item. When the dialogue says "Eww," that means that the corpse no longer has any items for you. Move on to another corpse until one of them gives you the etc item Brokkr's Necklace.
After that, you can show the necklace to the Old Woman in Vanadis 130 105. She will give you the Legendary Necklace of Brokkr, which is a wearable accessory.
The necklace provides seeking attack, which is a type of physical attack that never misses when performing physical skills. The higher the seeking, the less frequently you will miss when attacking.