One way to check is to go to PC > Verify Received Invoice. Enter the WIP number then click Refresh. If there is PC number and the state and status fields are X then it has been verified. However, once verified the order record is consolidated. The PC invoice is only retained for the number of days set in the parameter. So you might not see the record here.
Another way to check is in Nominal Ledger.
Take note of the WIP number, Supplier code and Cost Price of the Sublet
Go to NL > Transaction Enquiry > Current Transaction file (or Archived transactions)
Enter the WIP number  in the Suffix field. This will depend on the suffix format of each company. In this example, the suffix is in this format WIP + [WIPNO]. In some companies, it is just the WIP number. Click Proceed.
Search result will display the WIP number, Cost Price and the PC Invoice number if the sublet has already been verified.