There is a bug in the Dynamic Content creator, however. When you use the drop down to select the contact’s “Contact Type” it gives [[ contact.contact_type ]], which always returns undefined, presumably because there is no such field name.
The old-fashioned way … trial and error. I looked at the different syntax schemes applied to different fields in the Dynamic Content generator and tried each with the contact type field. [[ contact.type ]] worked with the Dynamic Content previewer, so I assume will work in other places.