public class GameMainMenu : UIClass
{
    public class JetPack : UIClass
    {
        public static UIPath UIPath = new UIPath("UIPrefabs/GameMainMenu/JetPack/JetPack.prefab");
    }
}

BindingFlags flag = BindingFlags.Static | BindingFlags.Public;
Type type = Type.GetType("GameMainMenu+JetPack");
System.Reflection.FieldInfo key = type.GetField("UIPath", flag);
Debug.Log((key.GetValue(null) as UIPath).ToString());