Keyboard is not working on iPad

You don’t mention the type or model of external keyboard that you are using with your iPad.

Apple Magic Keyboard for iPad, or an Apple Smart folio keyboard

Remove the iPad from the Keyboard - and carefully/gently clean the smart connector contacts on both the iPad and keyboard with a soft pencil eraser (a drafting-film eraser is ideal). Ensure that the contacts on both iPad and keyboard are dirt and dust free - and all debris from the eraser have been removed - before reconnecting the two.

If you can't connect your iPad to your Magic Keyboard, Smart Keyboard, or Smart Keyboard Folio - Apple Support

Bluetooth Keyboard

Delete the existing pairing from iPad settings:

Settings > Bluetooth > [My Devices] Bluetooth Keyboard Name - tap the blue “i” icon, then select Forget This Device

Next, force restart your iPad:

Force restart iPad (models with Face ID or with Touch ID in the top button)

If your iPad doesn’t have the Home button, do the following:

1. Press and quickly release the volume button nearest to the top button.
2. Press and quickly release the volume button farthest from the top button.
3. Press and hold the top button.
4. When the Apple logo appears, release the top button.

Force restart iPad (models with the Home button)

Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.

After restarting the iPad, re-pair the Bluetooth Keyboard with your iPad. Refer to you Keyboard’s User Guide for the pairing procedure.

On-screen Keyboard

If the screen isn't working on your iPhone or iPad - Apple Support

Assuming you mean the on-screen keyboard:

If the screen isn't working on your iPhone or iPad - Apple Support