Look at the example in Example 1: Retrieving cost center and pay group information. Seems the correct XPath would be wd:Worker/wd:Worker_Data/wd:Organization_Data/wd:Worker_Organization_Data[wd:Organization_Data/wd:Organization_Type_Reference/wd:ID[@wd:type='Organization_Type_ID']='COST_CENTER']/wd:Organization_Data/wd:Organization_Code/text()
Let me know if that helps.