AOT(Expense report) - How can I find Expense report in WorkflowWorkItemTable?

Hi everyone,

I am using SysWorkflowApprovalService.applyAction method in order to approve or reject Purchase orders (PO). At the moment, I am able to approve/reject PO as can I see the status change in WorkflowWorkitemTable (WWT). 
Now I want to approve/reject Expense Reports (ER) but I can't see any listing of ER in WWT. Why is that? Is it hidden? 

SysWorkflowApprovalService.applyAction method has 5 parameters (action, network, workitem, domain and comment). For 'workitem' parameter, it asks for WorkflowWorkItemInstanceId Extended Data Type which is related to 'Id' in WWT.  

Now, my question is, How can I get the id for Expense Report? 

Please feel free to ask any questions. 

Cheers,
Sagar