Which token would a marketer use to include a unique access URL in a webinar...

To include a unique access URL in a webinar confirmation email, the marketer would use the {{member webinar url}} token. This token is a type of Member Token, which is used to insert unique values from integrated services partners. A common use of Member Tokens is for unique URLs for webinar attendees. Each person has a unique URL to access the webinar that can be inserted using the {{member webinar url}} token.The marketer would need to create a text token called Webinar Key in the My Tokens tab of the Marketo webinar program, and copy the webinar ID from the integrated service partner (such as GoToWebinar) into the Value box. Then, the marketer would use the {{member webinar url}} token in the confirmation email content.

References: Tokens Overview | Adobe Marketo Engage - Experience League, How to: Use Marketo My Tokens and Templates to Scale Webinars - Sponge, How to: Manage GoToWebinar Simulated Live Events in Marketo - Sponge