Considering I've never seen a login option for nickserv, unless this is an option that is for IRCops only, you're going to have to clarify just what it is you want.
If this is something for IRCops, and you are an IRCop, then you'll have to supply the proper format for the login.
Most people, when referring to nickserv, are looking at the identify command, in which case the following will automatically identify you to nickserv when you connect.
.msg nickserv identify <password>
Replace <password> with your actual password