I don't think it's an option you turn on and off. I think it should just show (unless you removed the code from your template). Try this:
Create a new style with no parent:
- Styles & Templates > Style Manager > Add New Style
- Parent Style: No Parent Style
- Title: Default vBulletin
- Allow User Selection: Yes
- Save
Then browse the site using that totally default vbulletin style - can you see it now?
To change the order inside a thread, you set that in your User CP. There may be a modification to do it in a thread, I don't know, try doing a search in "all mods" "titles only"