Danny had mostly resigned himself to life as a pawn for one cosmic force or another. Mephisto, Zadkiel, God, whoever was pulling the strings here... He'd given up hope of ever really cutting the strings. Every time someone managed to do that, the puppetmaster just got replaced by some new manipulator. That didn't mean he liked it, but fighting against it was something that he mostly considered pointless. Though maybe that was the hopelessness talking.
How did they stop it? That was a damn good question. Danny didn't have the first idea how to stop the apocalypse. Still, he wanted to give Tess something to hold on to. He knew from experience what could happen when you felt like there was nothing. "Don't know how to stop Lucifer himself, but his demon buddies, that I do know. Last time I was here some guy out in...one of the Dakotas, I don't remember which, did this training thing. I remember most of it." He hesitated a second, frozen in indecision. He could just tell her to ask the heads of the complex, or if the Winchesters weren't so busy he could tell her to ask them.
He couldn't stand there thinking about it forever. He basically flipped a mental coin and said, "They've got classes here for self-defense. Things called devil's traps, to trap demons. It's a big occult pattern in a circle, and if you get a demon in there, they can't get out without someone or something breaking the circle. Real specific pattern, though, and if it's even a little off it's useless. They also teach you the Latin and give you some holy water and stuff." He glanced at her and added, "But if you wanna stop it, you have to learn the other stuff. Hunter stuff. Don't know if they'll be teaching that anytime soon, but you could ask. Or I could show you a few things that I remember from the camp, whichever."
He nodded as she described what she'd seen. "Yeah, it's kinda like that, except the demons physically invade your body. Usually through the mouth. Once they're in, you're locked up in a little cage in your head. Maybe you're lucky and you don't see what they're doing, but most of the time, you do. And those of us with powers, the minute they're in you, they can control the powers, too." He put just a little emphasis on the word 'us' there, a subtle confession that she wasn't the only one in the room with powers.