Thanks for reaching out to us. You can check your Invoices by going to the Transaction History and click on the Ref ID as shown in this screenshot. From there, you'll have the option to download a PDF file with the Invoice that includes Payment processing fees as shown in the screenshot here. I hope this answers your question. Feel free to follow up if you have further questions.
I asked about this a couple of days ago. It seems that Upwork does not issue invoices to its clients for the transaction processing fees that it charges. It only provides receipts.