update: I have check spelling on under settings for both keyboards.
Please try and not misunderstand this question. I'm NOT talking about the white background word suggestions white typing.
I believe before iOS 10 if a word had a red squiggly if you tapped it you would get a black tooltip with a suggestion.
Can this be somehow turned on again? I don't see anything on the web even mentioning it, it's like noone noticed it! (The black tooltip does show up still but only in the case you type a word and hit backspace.)
I can add screenshots if you guys need it.
Like I've mentioned in the comment to the first answer, I have check spelling on.
Best Answer
The feature you're talking about is called spell check, and is different to the automatic spelling correction that occurs when you type.
It still exists in iOS 10.
To make sure that it is enabled:
Settings > General > Keyboard > Slide "Check Spelling to on"
If it is already enabled, I would recommend disabling it, restarting, re-enabling it and then restarting again to be sure.
Lastly, make sure you are using the default Apple keyboard by going
Settings > General > Keyboard > Keyboards > Ensure "English UK" or "S" is checked.