How to open Resolution Center for an app version rejection after the app is approved?
Found this floating around on Reddit.  I've also had the same issue and was able to find the Resolution Center from this: 

https://itunesconnect.apple.com/WebObjects/iTunesConnect.woa/ra/ng/app/[your-app-id]/platform/ios/resolutioncenter

Update it with your AppID.  This ID is for iTC, not the bundle_id from the developer portal.  You can find it in iTC and it will be a series of numbers.

UPDATE

Since iTunes Connect has become App Store Connect, due to redirects, the above URL no longer works. Please use the following:

https://appstoreconnect.apple.com/WebObjects/iTunesConnect.woa/ra/ng/app/[your-app-id]/platform/ios/resolutioncenter