Re: assassin secondary job Correct description of 'Core' vs 'Prophecies' vs 'Factions' skills.
Summary: If you have both chapters on your account, you can use any skill you can find in the game on any character. If you only have Chapter 2, you'll only be able use Core skills + Factions skills, and in theory I would have thought that Anet wouldn't allow you to unlock Chapter 1 skills (but mabye that's what the trial key was for).
I beileve guildwiki has a complete list of 'core' skills by profession, and I'm slowly updating the Alliance wiki with this information as well (only got Warrior done so far).
Also all the classes in Chapter 1 are considered 'core' professions, so Chapter 3 will have the original 6 plus whatever new classes Anet has in the works, and possibly NO new Assassin or Riutalist skills (pure speculation).