I am missing a Developer option under Settings menu. What do I need to do to make it appear?
In versions of Xcode prior to Xcode 6, you can connect the device to your computer over USB, open Xcode → Organizer and select Use for Development.
Use for Development was removed from Xcode in Xcode 6 and later. It is no longer possible to do this for devices using Xcode 6 or later, even with the Devices page (⇧⌘2).