[snbzk]

Based on your elaboration of the story, I'll update my revision:

"You say that we, who are at the mercy of the gods, try to escape fate desperately to survive or try to achieve our ambitions while, all around us but just out of sight, necromancers and strange monsters who came from nowhere are struggling for power to dominate the whole world?"

I tried to make it sound like normal people could see the necromancers if they would just turn and look at them, but because of the psychic barriers people simply don't notice.

"Struggling for power" sounds more like the necromancers are actively fighting each other for power. You could also say "grappling for power" if you prefer.

Originally Posted by YuriTokoro

He didn’t know the information. He hates what he just heard.
What he heard was the necromancers and monsters are trying to conquer and govern the world. If you heard that, and you had known there were some necromancers and many wizards in the world, what would YOU say?

I would probably say "What can we do?" or "We have to do something!", but that may be more than what Skarr actually said. "I had no idea..." is closer, followed by something like "Skarr grimaced" to emphasize his anger/concern. I can't really think of any short spoken phrases that convey the right emotion and fit the tone of the preceding sentence, so if I were translating the book I might have to do more than just convert the sentence directly.

Do you say “No kidding.” when you are praised and dispraised?

If someone gives you a compliment, you could reply "No kidding?" in question form if you wanted to be cute. It sounds like you're asking the person to flatter you some more.

You could also use the phrase in a self-deprecating way if someone criticizes you:
"Yuri, you're really terrible at karaoke. "
"Yeah, no kidding. "
It simply means that you agree.

When you say “Really? No kidding.”, does “No kidding” mean like “I’m surprised.”?

Right. In that case it's sort of a rhetorical question asking "You aren't joking, are you?" The "..." at the end is essential, though, because the tonal inflection is different from just "No kidding," which is a statement.

In the same situation you could also say "Really? No kidding?" which is a question that requires a response. It, too, has a different inflection and means that you're surprised but also slightly skeptical.