Keynote doesn't work on my iPad

Are you having difficulty (a) opening the App itself, or (b) an existing presentation?

a) Unable to open the Keynote App

Begin by "offloading" the Keynote App from your iPad. This procedure will uninstall the App - but will not remove associated App data or files from your iPad:

Settings > General > iPad Storage > Keynote > Offload App

After Keynote has been offloaded, perform a forced restart of 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.

When your iPad restarts, you can reinstall the Keynote App:

https://apps.apple.com/app/keynote/id361285480

b) Unable to open an existing Keynote Presentation

Open the Keynote App; as test, create a new Keynote presentation and save/close the presentation.

Re-open the test Keynote presentation. If all is working as expected, you can attempt to open you original presentation file; if the original file won't open, it is likely to be corrupt.