Let me give you a quick rundown on getting that cleanrot set. Start from inner aeonia grace in the swamp, and make sure you've got your silver scarab talisman equipped for better drops. Riding torrent through the swamp is basically essential since you don't want to deal with scarlet rot while farming, and you'll spot the knights pretty easily from skull markers on the ground.

The best route is circling through the southern edge where you'll find about 4-5 knights clustered together, then sweep northeast hitting the ones near the big roots. Good to know that using fire or lightning really helps take them down faster, and keep flame cleanse me ready if you get hit with rot. The knights drop different pieces randomly - helm, armor, gauntlets and greaves plus their weapons if you're interested in those too.

You might need to run this route a few times since drop rates aren't amazing, but with the silver-pickled fowl foot and decent arcane, you're looking at maybe 30 minutes to an hour for the full set. Just rest at the grace after clearing the area and repeat until you've got everything. If you're in late game, there's also a single knight near the prayer room in the haligtree that's easier to farm, but the swamp route is generally faster for the full set.