If you're referring to reports, we're currently unable to customize them in QuickBooks Online (QBO) to display the Tax percentage and export them to Excel.
In the meantime, we can manually enter the tax percentages in Excel or format the cells. Here's how to locate them in QBO:
Go to the Sales tab and select Invoices.
Select the invoice and click Edit invoice.
Under the Tax column on the Invoice page, you'll see the sales tax.