The Cat School Witcher gear is pretty nifty set of armor to have on you once you’ve hit level 15. The level recommendation for this scavenger hunt quest is level 17, but if you’re familiar with the combat system and Sign usage in The Witcher 3, you can tackle it as early as level 15.
To unlock this quest, head over to Est Tayiar, which is on the eastern side of Velen. There, you’ll find the Cat School notes hidden in the ruins. You’ll also visit this area during one of the secondary quests for Radovid so you can grab it then. You’ll also find your first gear diagram for the Feline Silver Sword there.
Next, you’ll want to fast travel to Castle Drahim. Use the Aard Sign to break through the castle doors and head straight down to the basement. There’s quite a bit of loot to be had here, so take your time to clean the area out and be on the lookout for two items pertinent to the scavenger hunt. The first is the gear diagram for the Feline Steel Sword, and the second is a journal that gives you your next location. Read it, and it will reveal that there’s another gear diagram to be found in the wreck of the Flying Stag.