Symptoms

When using the SharePoint 2013 wizards in the K2 Designers, there is a drop-down that is used to indicate which site collection the wizard is supposed to affect. When attempting to set this field, the drop-down is empty or does not contain the site collection needed.
 

Diagnoses

This issue likely stems from the fact that the K2 for SharePoint 2013 app has not been added to the correct site collection. In order for the Site Collection to be listed in the drop down of any of the wizards, the K2 for SharePoint app must be added to the Site Collection you wish to interact with.
 

Resolution

Documentation on how to add the app to a site collection is available here:

http://help.k2.com/onlinehelp/k2forsharepoint/ICG/current/default.htm#Install_Topics/OnPrem/Add_App.htm