How do I print from iCal on iPad Pro?

There really is no native print button in the Calendar app in iOS.

You can get an app from the App Store which can access your calendar and print from that app.

If you sync your calendar with iCloud, you can go to www.icloud.com on your computer and print the calendar from your computer.

Or the simplest thing to do, which is what I do if I need to print something quickly. I open the calendar app to the view I want, take a screenshot of that page and print the screenshot from the Photos App.