ATM machines are inherently open to fraud since they are readily available to the public and rely on screens to give out information. So, for your protection, you cannot find your account number via an ATM. This is for your safety as there are so many schemes to rob people of their cash at ATMs.
TIP: Shield the keyboard with your other hand when entering your PIN. There are lots of other ATM scams, but this technique can help prevent your PIN from being stolen.