I just got this knowledge entry on EU by getting a Millennial Wild Ginseng while gathering.
This may have been patched recently or is RNG since this is not my first Millennial Wild Ginseng drop on this account.

Where do you get this knowledge?

I see in database there's millenial wild ginseng but that's clearly not it since this is a rare drop from green thumb mini-game.

Then there's one white item named millenial wild ginseng which says you can get trading in Port Ratt... well, Port Ratt hasn't existed in a couple of years so.. I'm gonna guess that's not in game anymore.