Breaking this up a bit
As long as you have the OG setup with Blynk it will keep Blynk up to date upon change (and every 15 seconds) So if we know Blynk knows the status and is available via the internet.
TO RETRIEVE STATUS ON REQUEST
To get status you just do a normal web request (HTTP GET) to http://blynk-cloud.com/auth_token/get/pin (https://blynkapi.docs.apiary.io/#reference/0/write-pin-value-via-put/write-pin-value-via-put)
Where auth_token is your blynk token and pin depends on what you want to read the door state its virtual pin 0.
So you need code that takes the request of “Is the door open” and then makes the request to Blynk to get the value of the pin and then returns the status.
TO CHANGE STATUS ON REQUEST
Same thing here accept the request is http://blynk-cloud.com/auth_token/update/pin?value=value