You do not have to specify the exact routing, just enough to complete the RTW trip back to your point of origin. You can leave all segments except the first open. If you do add or delete cities along the way then you will have to have the ticket reissued at a cost of $US75 and some added hassle. If you specify the total route (open or booked, either way) at the front end, then you can just make date/time/flight changes at no charge.

As for a format, something like -

X/O [date] origin, destination airline [flight]

Where X/O indicates transit/stopover and items in brackets [] are optional, depending on whether or not you are actually booking the flight.