Hey there Zhiyuan96,
Thanks for reaching out to the Apple Support Communities. To get started, it looks like this may be the Shortcuts Bar that is providing suggested words when using an Apple external keyboard with your iPad.
For more details on this bar, and how to disable the Predictive Text from appearing, check out the steps below from the following resource: Use shortcuts on an Apple external keyboard with iPad - Apple Support
To turn off the suggestions, go to Settings > General > Keyboard, then turn off Predictive Text.
Let us know if that's able to help.
Take care!