How to show registered users the ability to add title

The way codinghorror has ‘cofounder’ - how can I have this field for all registered users (and preferably during onboarding)?

I am on V. 1.7 beta.

The title can be assigned by badges or groups.
Some badges can be use to add a (predefined) title. You can add a new badge, and set this badge to display a title.
Every user who grant the badge can add a (predefined) title from the profile page.
Go to /admin/badges and create a new badge
You can use this query to grant the badge for all Trust-level 1 users (you can change the number for other trust-level)

SELECT user_id, granted_at
FROM user_badges
WHERE badge_id = 1

Trigger daily.

This is the easy way, and you can add more badges, see here [Superseded] What cool badge queries have you come up with?

There’s no way to let the users add a custom title. This is an ability reserved to admins and mods.