Are you trying to make auto-correct give a suggestion, but it won’t appear?

Make sure to use the on-screen keyboard to do the typing.

It turns out that iOS knows if you are typing on the on-screen keyboard or a physical keyboard. If you are using a physical keyboard, it won’t present suggestions.

This held true for both the simulator and the device.  When I tested using the simulator, the keyboard on the computer would not cause suggestions.  When I tested using a bluetooth keyboard with an iOS device, it would not cause suggestions either.