If you're logged into a Square Enix Members account, you can see how many Reward Points you have by clicking on your name in the top right-hand corner of any Store page to display the account drop-down. The total amount of points will be displayed at the top of that sub-menu.
For further information on your Reward Points, just click on your points in the account drop-down to get to the Points Balance section of your account. Here you can see which rewards are available and an overview of your rewards history.