How can I establish if I can travel back via nottingham please ?
The easiest way for a non-technical person would to be to use a booking engine like National Rail Enquiries to see if you are offered an itinerary on the same one ticket as you have purchased. If you are offered multiple tickets or no ticket at all then it is unlikely to be valid (though booking engines occasionally get this wrong).
It appears that, in this case, it is not permitted to travel via Nottingham. The furthest-north station on the Nottingham-Worksop "Robin Hood Line" for which travel via Nottingham is permitted is Mansfield Woodhouse.
Of course it is possible that the guard on a service southbound to Nottingham may accept a ticket from Whitwell as valid, but I certainly wouldn't assume it, and accordingly you should ask the guard before boarding the train if you intend to do this, whether or not they will permit you to travel via Nottingham.
Can I brake the journey on the return leg of this ticket ?
Break of journey is permitted on the outward and return portion of almost all walk-up tickets, and tickets from Whitwell to Manchester are no exception. However, you may only break your journey along a permitted route so it would not be permissible to break your journey at Nottingham on this ticket (unless you were specially authorised, preferably in a written endorsement on the ticket, to do so).
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