IPad How to turn on screen recording

Start here:

Record the screen on your iPhone, iPad, or iPod touch - Apple Support

Are you unable to enable this feature from your iPad Control Centre?

Settings > Control Centre > [More Controls] Screen Recording - 

Use the green “+” button to add this feature to available controls.

Next, check your ScreenTime restrictions:

Settings > Screen Time > Content & Privacy Restrictions > Content Restrictions > [Game Centre] Screen Recording - set to Allow