There is no way to see that online but if you sign up for email communications and use a current email address, you will get a monthly statement that includes the expiration. If you are concerned about miles expiring, download the toolbar and do some searches (there are a couple of threads on that topic in this forum) to get some free miles, or buy something from Amazon thru the shopping portal as those may credit faster. Groupon seems to consistently credit quickly too.

On the website you will see a Contact US link; this will take you to a customer contact form which will take your input and email it to customer service.