You can manually open the purchase order if you're referring to the linked transactions you make against your PO. Just click on the link below the status of your PO to open the transactions you created. I've attached a screenshot for your guide.
Also, QuickBooks Online has several reports that can help with your search. If you're referring to something else, you can check this related article to learn more about how PO works in QBO: Create purchase orders in QuickBooks Online.
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