Hi David,
On the mentionned step in the workflow you can see that your task has no agent assignment meaning there is not potential agents, also there is no expression for the determination of the agent [agent] on the step but this is standard here I will explain later.
First go to PFTC in the menu
the either you choose attributes button to put it as general (meaning every one is a potential agent : be carefull with that as in case the agent determination can not find an agent and the rule does not trigger an exception then the workitem is sent to all the potential agents)
The other choice my favorite is to assign a role (PFCG role) or an organisation from the PPOME) by clicking on the button 
Now that you have told the workflow who are the potential agents, lets take a look at what SAP provided you for the responsible or determined agents.
On the main screen for the task in PFTC
Go the default rule tab you'll be able to check that SAP has provided you with the determination rule AG 20000027
So everything is fine as soon as you have set up the release strategy and the agent assignment.
Have fun with the workflow !
Cheers
Stephane
PS: for more information of course consider the book on workflow in SAP Press and for agent assignement you can check http://scn.sap.com/community/bpm/business-workflow/blog/2015/10/30/agent-determination