Indeed, the toilets referred to are accessed from the Southern Concourse (ie from outside the ticket gates). They are 'pay to enter'.
They are shown on this schematic from the EMT website on the pages numbered 12 and 16 in the PDF:
https://www.eastmidlandstrains.co.uk/Global/Documents/Nottingham Station LP guide updated for website.pdf
Ah, I didn't know that. Given that the Southern Concourse is fairly new, presumably it should be well equipped with CCTV?