The parameters are stored in Service Request Parameter (Business Object: ServiceReqParam) and can be accessed via the Relationship ServiceReqContainsServiceReqParam:
Service Request Parameter stores the parameters in key/value pairs, ParameterName and ParameterValue. ParameterName is the Unique ID of the field, as specified when you created the Request Offering:
So if your field unique ID is 'Name', and you want to prompt for the searcher to select the name from a list of employees (the second parameter to Prompt() is the Pick List name; use the same one as you did when you created the field on the Request Offering), you could do something like:
Hope this helps!
Thanks so much Terry - that worked perfectly