How to get the bar under the text messaging square that complete the texting.

You can turn the suggestions on/off by going to Settings > General > Keyboards and turning Predictive to on. If already on, try turning off and then back on.

Another method is to tap and hold on the keyboard switch key (e.g., emoji key).

If there is a thin gray bar with a white dash in the middle of it immediately above the keyboard, you can reopen the suggestions by sliding up with one finger on the white dash. May take a couple of tries to get it to reopen.