To enable the Roll Class view on the checkout page, it must be enabled on the extended patron attribute.
Step 1 - Navigate to the Extended Patron Attribute
Go to KOHA administration > Patrons and circulation > Patron attribute types.
This will take you to a new page with existing patron attributes on your site.
Go to the Rollclass patron attribute on click the associated Edit button under the Actions column.
This will open a new page with a form of information related to the existing patron attribute.
Step 2 - Enabling Rollclass at checkout
Ensure there is a tick in the box to the right of the line Display in patron's brief information, highlighted below and click Save.
The Result
Once this functionality is enabled the Rollclass will be viewable on the checkout page as indicated in the example below:

This is a system wide change so the Roll Class will show up for all patrons that are assigned one.