I got this from public notice from the National Identity Management Commission (NIMC), Nigeria,...how to retrieve your National Identification Number (NIN). Details in the photo below.
NB: They said (and I also saw it myself when I dialed the number) that the service costs N20. So be aware.
And I please I don't work there . Contact them for any/every info you need.



The National Identity Management Commission (NIMC), was established by the NIMC Act No. 23 of 2007, and the NIMC has the mandate to establish, own, operate, maintain and manage the National Identity Database in Nigeria, register persons covered by the Act, assign a Unique National Identification Number (NIN), etc.