You can check your remaining subscription time using the /subscription view command. If you've never had a subscription it will say None otherwise it will provide you with the Relative Time from Discord to when it does or did expire.
Paying/Extending Subscriptions
You can pay for your subscription using the /subscription add command and providing the amount of Months you with to pay for. This will generate a XUMM transaction link and QR Code for you to sign/approve.
Once your payment is verified, your subscription time will be added and you can check again with the /subscription view command. Enjoy those extra collection and role spots!