The lizard you find in the Dark Swamp and eventually take to the Misty Abyss is Nauxus. His story progresses around an amulet and you do not give him a cleansing water to talk to him or advance his story. The Between Worlds event in the Events log should help you with Nauxus.
It sounds like you are talking about Xeroth (Xer), the self-exiled lizard you meet at the Corrupted lake. You can give him a cleansing water to keep him talking. There is a lot more to do with Xeroth. Visit him in his underground Hideout to advance his story.
There is more with Logan in both .31 and .32. You will find it after you start the Bareshade's Expansion event. He also has a role to play in the Country Road event.
You don't need to check on him until then, best I recall, but when in
Bareshade I think it is always a good idea to check on everyone and look
in Talk and Task. Same for any other location.
It costs no game time to check on Talks and Tasks, and I learned the
hard way to check everyone I can any place I am. Sometimes the most
unexpected character has information or a task that advances the game.
There may be other times to interact with Logan if you encouraged him to go to the Bandit's Camp, but they don't advance his story far as I remember (they are sex scenes you can see or take part in).
