I've got an iPad2 that's supposedly susceptible to the latest encryption hole in iOS 7. However, it's not offering me the update automatically. Where can I go to force it to check for updates?
To check for it manually, go to Settings -> General -> Software Update.
Your device will then check with Apple's servers and let you update if there is newer software available, otherwise it will show you the current version and tell you that you're already up to date.
The update are pushed over the air (OTA) by Apple. There's not much you can do except checking yourself when you know there is an update since the push notification servers have to churn through lists of all the devices they think are needing the update and might have to retry a few times if your device doesn't receive the first message notifying it of a new update.
It's often the case that Apple don't roll out each update to every device in every country at the same time. You may find that it takes a few hours (or even days) to appear as available on some devices. I would suggest trying to update via iTunes which usually allows you to install updates immediately.
imore.com usually has up to date information on releases.
My iPad 2 had an earlier update downloaded that I'd never installed (7.0.4) and Settings -> General -> Software Update didn't offer 7.0.6.
I powered down and booted up, then it downloaded the latest and let me update.