The Subcontractor card in your Dashboard gives you an overview on subcontractor purchases orders for your active jobs:
The Open PO tab of this card shows different open contracts with subcontractors that have not been fully billed yet. The subcontractor's name is on the left, and the PO# of the contract is on the right. Clicking the sub's name will open up the PO's details page.
The No PO Yet tab shows jobs in Knowify that have a subcontractor budget and no subcontract added yet.