eGift Cards will usually have instructions listed on them for how to check the remaining balance, which may also be found under 'Terms & Conditions'.
However, if that is not the case, there are a few other ways that you can check the remaining balance on your eGift Card:
You can ask a staff member in store. They can scan the eGift Card for you and see what the available balance is.
You can go on the store's website and there will be a section for eGift Cards where you can check your balance.
You can ring the eGift Card Support number. This number is usually displayed on the store's website.
If you use an eGift Card for your purchase in store, the remaining available balance may be printed on the bottom of your receipt (Note: this is not the case for all stores).