Sorry, there is no single command that universally spawns quests.
Whoever releases a quest should either indicate the method of spawning the quest givers and items, etc. or provide an .XML and/or .CFG file for handling the spawns. Unfortunately, this is not always done. You can either go to the original creators for help, or post a complete list of the quests you need help spawning and someone who has one or more of those quests might be able to get you the files you need.