How does one copy keychain passwords from one iPad to a new iPad?

If you have not enabled Keychain yet, you must be using two factor authentication in order to use Keychain.

Set up iCloud Keychain - Apple Support

I copied this blurb from the linked article above.

How to turn on iCloud Keychain

Before you turn on iCloud Keychain, update your device to the latest iOS or iPadOS, or the latest version of macOS, and turn on two-factor authentication for your Apple ID.

Assuming that both old and new iPad are signed-in with the same AppleID - and you have enabled iCloud Keychain on both devices - your Keychain will be synchronised between devices:

iPadOS16

Settings > [Your Name / AppleID] > iCloud > Passwords & Keychain > Sync This iPad - set to ON

iPadOS15 and Settings > [Your Name / AppleID] > iCloud > Passwords & Keychain

Settings > [Your Name / AppleID] > iCloud > iCloud Keychain - set to ON