the wbl-file is something you create in adding white- or blacklist-entries.
it's a list of wanted or strictly unwanted emailadresses. adresses (or whole domains) that are in your whitelist, pass spamassassin without processing. on the other hand, adresses on the blacklist will not be processed either, but deleted. so be careful with that feature!
as you can imagine, it's no use if i send you my wbl, cos there's only my personal entries of adresses, which are no use for you.
think, what you mean, is a list of known spam-adresses. they are looked up in the razor-blacklist (included in spamassassin - has to activated), and learned by spamassassin as well (has to be activated, too).
so... if you recieve unwanted mails that always pass the scanner without being tagged as spam, you can add the adress to your blacklist. or if mails from your friends are marked as spam, though they are not, add the adress to your whitelist.
hope that helps
cheers, thorsten