Answers for "All methods in an abstract class must be declared as abstract methods."

can you declare an abstract method in a non abstract class

No. A normal class(non-abstract class) cannot have abstract methods.

Class must be declared abstract or implement methods 'hasVerifiedEmail'

You need to either extend Illuminate\Foundation\Auth\User instead of 
Illuminate\Database\Eloquent\Model, or use Illuminate\Auth\Authenticatable 
trait in your class

You need to extend Illuminate\Foundation\Auth\User like this

use Illuminate\Foundation\Auth\User as Authenticatable;

class User extends Authenticatable
{

}