i would suggest adding a small icon to each kingdom on the worldmap - when u finished all challenges with 5 stars.
when i finished all challenges in one kingodm, i have to check manually what kingdom has one or more challenges open.
this could be changed with a small icon like for example a green checkmark added to the kingdoms to mark them as “Mastered”…
just another impression - lets talk about this 
Yeeesssss! I actually keep a handwritten list in a notepad to show what kingdom challenges I have to finish.
There is already a notification for unfinished story quests. Why not just apply that to challenges also?
I like that idea.
You could go either way, put a sword icon if there is challenges remaining to do, or put a shield up to show you are finished.
A smaller and less flashy approach would be changing the Twin-Swords icon for challenges (when selecting a kingdom), would be adding a goat skull or shield to the icon.
So you’d still need to select each individual kingdom, but save heavily on loading times.
Or spilt the exclamation point for new quests with a different symbol and color like acesions and traits.
That way you can tell if new quests release (such as classes) or if you have one or both left to do
I understand the annoyance of searching through each Kingdom to see which challenges you have left (and I had my own handwritten list too).
However, I think a marker as obvious as the quest marker would encourage new players to charge through the challenges, when arguably they’re better off waiting until they have Celestial armor to finish them all. New players are much better off focusing on the Quests to unlock storyline Epics and hero classes than thinking Challenges are a good thing to finish early.
I like @Zelfore’s idea of a marker that is clear, saves loading times but isn’t flashy and obvious on the main map screen.
Add an Asterisk (*) to the name of the Kingdom when challenges are available. And yeah the “! in the shield” is already on the map for available quests.
Or hell have something like this on the icons for available challenges:
I liked the idea of using the shield icon but colouring it two different colours (like the split colour icon for upgradable troops currently).
Eg. Blue shield for challenges remaining, red shield for quests and both (colour split down the middle) for quests and challenges remaining.
Sounds like a lot of over-complication imo. If you display urgency, players will feel like they’re required to power through challenges and reasonably earn something from it. (Other than souls.)
A subtle change to what’s completed instead of what’s unfinished would be a safer way to go about this.
that is why i suggested to just show a small green checkmark when u completed all challenges…
dont show something when u have challenges or quests open, it should be a symbol for a 100% completed kingdom where nothing is left open^^
