You can find the code on your profile page, more precisely in the Settings: by clicking on it, a new screen will open with the unique QR Code, ready to be shared and which will allow the recipient to add WhatsApp with a single click.
Android
Open WhatsApp> go to More options> Settings.
Tap the QR code icon next to your name.
iOS
Open WhatsApp> Settings.
Tap the QR code icon next to your name.