here is something that i use, key is to get a queryable reference to the workitem type property and compare it with the specific workitem type ID.

//Create the Term
Term queryTerm = new Term(Operator.AND);
 
//work item type ID to be used to filter     
var mWorkitemType = "workitemtypeID";

// gather a queryable reference to the Workitem Type property for this ProjectArea
IQueryableAttribute workItemTypeAttribute = factory.findAttribute(mProjectArea, IWorkItem.TYPE_PROPERTY, mAuditableClient, mMonitor);

//build the attribute expression using the queryable reference to type property and the filter workitemtype ID
AttributeExpression exprnWorkItemType = new AttributeExpression(workItemTypeAttribute, AttributeOperation.EQUALS, mWorkitemtype);

// add the expression to your query term
queryTerm.add(exprnWorkItemType);

// run the query and capture the results
IQueryResult<IResolvedResult<IWorkItem>> queryResult =
                mQueryClient.getResolvedExpressionResults(mProjectArea, queryTerm, IWorkItem.FULL_PROFILE);

Use the ID from the process configuration Work Item Type editor as String. For instance, for a defect:

//following the code from "Developer's Guide to Querying Work Items"...
new AttributeExpression(
                findAttribute(projectArea, auditableClient, IWorkItem.TYPE_PROPERTY, null),
                AttributeOperation.EQUALS,
                "defect"
        );

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Gabriel Enriquez, IBM Rational, Tracking & Planning