@nshukor there are only two ways I know of:
1. You should receive an email from SAP Concur stating that a payment has been made.
2. Login to the AMEX website to check your statement.
This is a little tricky to answer without knowing more about your configuration.
I would recommend opening the expense report and then looking for the menu item that shows payments - which may or may not be used by your company.
In the NextGen UI, this is under Report Details - Report Payments
In the older UI, this is under Details - Report Payments.