Hi!
A great starting point is our Themer’s Guide, which explains the basics for safely overriding and customizing our templates:
Themer’s Guide
In this case you’re probably going to be interested in the email.php template, the original being located in:
the-events-calendar/views/tickets/email.php
The trick is to work back from the ticket ID – available as $ticket[‘ticket_id’] within the loop. That represents a post which has a piece of post meta attached to it called _tribe_wooticket_product … in turn this is the ID of the underlying WooCommerce product and provides access to the ticket description:
$product_id = get_post_meta( $ticket['ticket_id'], '_tribe_wooticket_product' );
$product = new WC_Product( $product_id );
$description = $product->post_excerpt;
To save yourself from reinventing the wheel you might also leverage a library of existing code like this (unofficial) one.
Beyond that, we’re always interested in new feature requests if you think others would like to see this (or you could upvote any suitable existing feature requests).
Does that help?