I wanted to know if there any challenges I can make to this notice?
You cannot challenge the notice. It is simply a notice informing you that a prosecution is being considered.
If you mean can you challenge any prosecution that might arise from it, nothing you have mentioned indicates that you can. But then you haven't really told us much. Do you suspect that there are any grounds? For example:
Are you the Registered Keeper of the vehicle concerned and if so was the notice served on you within 14 days of the alleged offence?
Do you suspect the speed alleged is incorrect and your actual speed was lower than 50mph?
Do you suspect the limit was not lawfully in force or not properly signed?
Perhaps you could help us out a little here. Meanwhile, don't forget that, whatever issues you might have with the speeding offence itself (or the notice), you
must respond to the "Request for Driver's Details". This almost certainly accompanied the NIP and may even be printed on the same sheet of paper. Failure to respond in the 28 days allowed will see you commit a separate, more serious offence which, on conviction, carries six points and an endorsement code which gives insurers a fit of the vapours.