I just posted info about this in a recent Weekly Dynamic but the GP team also covers Adding Document Lines To A Notification In Workflow 2.0
Adding Document Lines To A Notification In Workflow 2.0 – Microsoft Dynamics GP Community
Install, Upgrade & AdminMicrosoft & the GP Ecosystem
Archived post from 2014. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.