The Weapon Connoisseur is a side quest in The Legend of Zelda: Breath of the Wild. It is a quest given to Link by Nebb at Hateno Village in the region of East Necluda. During the quest, Nebb asks Link to research and investigate special weapons.
The items you have to obtain, and the rewards you receive are as follows:-
6th Item - Ancient Battle Axe+ This drops off Guardian Scout III, which can be found at many of the "Modest Test of Strength" shrines and if a blood moon has passed, you can revisit and kill the enemy again even if you've already beaten the shrine. Show it to Nebb for a silver rupee.
7th Item Frostspear you can get this at the shrine in the Spring of Wisdom Jitan Sa'mi Shrine. You can also get it off a Stalnox in the Lake region, or from the Coliseum Ruins when all four Divine Beasts have been defeated. Show it to Nebb for a gold rupee.
8th Item Ancient Short Sword After completing the Robbie's Research side quest, you can purchase an Ancient Short Sword at the Akkala Ancient Tech Lab. Show it to Nebb for a diamond, and you'll finally complete the quest.