Bank sort codes are usually necessary for doing online banking and/or transfers of funds. Each bank has a unique sort code that identifies it. Nigerian banks are listed here at this site: www.bankers-telenet.com This link will help you find branch addresses and sort codes or take you to each bank's own website which will have the sort code listed.
This information isn't available on line. You could start with this list of Nigerian banks (you will need to use the zoom to read it) and look at their websites individually to get or ask for the sort codes. Or you could try contacting one bank and asking them if they know another way to get the information more quickly.