"What will happen if you are picked up on an arrest warrant and they won't extradite you?"
The arresting state will hold you for up to 90 days. If the State where the warrant is hasn't come to get you, you'll be released - until the next time you get picked up for something else and, potentially, held for another period of up to 90 days.
"Also, how do you find out which states will extradite you?"
There are NO States that won't extradite you. All States will extradite you to all other States.
Now, if you're picked up on an Idaho warrant in Oregon it's probably a lot more likely that Idaho will come and get you than if you're picked in Florida on an Idaho warrant, but there's no guarantees. If Florida happens to be holding an Idaho serial killer at the same time, and ID comes to get him, they may well choose to take you back at the same time.