With workdesk eFile management plus solution it is possible to jump from a document or a task as the initial source objects directly into the associated eFile, using the foreign key relationship from eFile to associated document or document to associated task.
First of all I wanted to ask you where you have taken this screenshot from, as this is a very old design and not looking like the rebranded one. Are you using old Workdesk documentation? PLease get the latest Workdesk documentation from http://docs.alfresco.com. The new screenshot would look like the attached one.
In the Workdesk Configuration Guide you will find a complete chapter "eFile Management Plus". In there you will find a section "eFile Management Plus plugins".
The requested plugin is that one:
Open an eFile which is associated to a document or a task
The required Alfresco Workdesk plugin that one: com.wewebu.ow.server.plug.owefileref.OwEFileReferenceDocumentFunction
Please configure that document plugin using Workdesk Configurator. In Configurator you can always press F1 having a plugin root node selected to show the related plugin help and description of subnodes and parameters of the plugin.