Most likely either you did not configure the directory integration, or you have something wrong in your configuration for that.
The Jabber documentation has a whole chapter dedicated to the directory integration, have you reviewed it? and configured the directory integration accordingly???
If not, that's your first step.
If this is a windows PC joined to the domain and call manager is LDAP integrated, Jabber/Windows should autmoatically search the LDAP or Active Directory (Given Windows Server in the backnd)
If the PC is not in windows domain then you will need to either (1) configure UC Service and UC Service Profile in call manager to specify directory source (Where Jabber can perform search against) Or (2) Configure jabber-config.xml file to specify the directory sources
Also there are two types of directory Sources
1) For Jabber for Windows and Jabber (EDI)
2) For Jabber for Mac, iPhone, iPad, Android (BDI)
They must have different configuration (in both cases - UC Service Profile Or jabber-config.xml)
You have to configure two directory sources for above two categories.
If you do not want to use LDAP or Active directory for Jabber to perform serach you can use UDS for performing directory search where Jabber can search Call Manager for Users. When using UDS, you can have one settings for Jabber for Windows and Mac, iphone, ipad, android - but at the cost of reduced information versus AD
I know this is a long answer, but hope this helps!!