Go to AP / Insights / Explore / Vouchers.  Click on the Filter icon, and filter on "Vend Invc" (might be called Tran ID) contains <whatever the vendor invoice number is>.  Click on Refresh.  Click on the invoice in the main part of the grid.  You should have a Preview window on the left of the Explorer screen, and it should be defaulted to 'Voucher Lines' - that will show in the secondary grid below the main grid, and one of the columns that you see there should be "GL-Acct".  That's it.