If you've not been able to find the Purchased page in the App Store app since updating to iOS 11, don't worry - it's just moved.
- Open the App Store app as before
- Navigate to the Today tab (tap the Today icon bottom left)
- Tap the circular picture of you/your account at the top right
- Under Account, tap Purchased, then My Purchases
It's as simple as that.
There's a search box at the top, which we highly recommend because your list is likely to be enormous. And you can choose between viewing all your purchased apps, or just the ones that aren't on this device.
In iOS 10 and earlier the Purchased page (which often comes in handy for redownloading apps that have been removed from the App Store) lived on the Updates tab, but Apple shook things up when redesigning the App Store app for iOS 11. You can read more about this in How to use the App Store in iOS 11.