Old Mugwort believes that if the Wargs are angered, they will send forth their leader.
'It's going to take awhile before the special meal I am preparing will be ready. What should I have you do in the meantime?
'Ah, I have it! Wargs are mean-tempered sorts of beast, and they're smarter than your everyday wolf... stronger too. That means that they can get angry, and if they can get angry, they can make mistakes!
'The logic of that all works out, I'm sure of it! Now, you listen well: go east! Go to the far side of Nain Enidh and search the wilderlands off the road near Ost Cyrn for Wargs; defeat all those you find! Let's get them good and angry, and their leader is sure to come forth, hungry to taste some flesh!'
Wargs can be found off the Great East Road on the far side of Nain Enidh, in the vicinity of Ost Cyrn.
Old Mugwort thinks that if you anger enough Wargs, they will call forth their leader.
Old Mugwort is at the camp on the eastern edge of Minas Eriol.
The Wargs are surely angry now, given your exploits in Nain Enidh, and Old Mugwort should be informed of your success.