Tanlorin makes a brief comment after finishing quest with House of Reveries in Summerset. I also recall that Azandar comments some quests either in Necrom or West Weald

He commented when I finished a volcanic event in Galen. Did not expect it.

OP is not asking for generic observations from companions while exploring. Like if you defeat a dolmen, or geysers (most companions have different dialogue for each different type of world event) or when you do something in regards to their rapport. What they're talking about is the very specific unique dialogues that can happen during certain overworld quests if you happen to have that companion out, and also do not have anything to do with that companions personal quest. I know which quest you are talking about OP, and was delightfully surprised when Zerithar commented on it. I actually have him equipped with the moon scythe thing weapon style you get in the end.

Isobel will comment a lot during the High Isle main quest as you progress through it. Walks I do believe has unique dialogue for the Necrom quests. Although I wouldn't be surprised if they added some Murkmire lines for him too. But I haven't tested that yet. Miri fangirls in the background whenever you talk to Sotha Sil during Summerset/ Clockwork quests. There's probably more, but I mainly use Zerithar to face tank for me, so I can't remember specifics.

High Isle, Necrom and Crown Store Companions have unique lines at the end of Chapter questlines and various other quests:

FlameDark wrote: »

OP is not asking for generic observations from companions while exploring. Like if you defeat a dolmen, or geysers (most companions have different dialogue for each different type of world event) or when you do something in regards to their rapport. What they're talking about is the very specific unique dialogues that can happen during certain overworld quests if you happen to have that companion out, and also do not have anything to do with that companions personal quest. I know which quest you are talking about OP, and was delightfully surprised when Zerithar commented on it. I actually have him equipped with the moon scythe thing weapon style you get in the end.

Isobel will comment a lot during the High Isle main quest as you progress through it. Walks I do believe has unique dialogue for the Necrom quests. Although I wouldn't be surprised if they added some Murkmire lines for him too. But I haven't tested that yet. Miri fangirls in the background whenever you talk to Sotha Sil during Summerset/ Clockwork quests. There's probably more, but I mainly use Zerithar to face tank for me, so I can't remember specifics.

Yes, I did some of Zerith-var quest with an character who done all of Northern Elsweir quests and it was an comment about you knew how the hidden moon was destroyed who made me curious. Yes remember the quest then doing it again but did not remember the hidden moon part.