Symptoms

No K2 in Central Admin or Site Settings
 

Diagnoses

K2 for SharePoint 2013 doesn't need to be activated from the central admin.
The client was trying to use SharePoint 2010 integration and they have SharePoint 2013 instead, as he's using K2 studio on his own machine "client Tool" he didn't have the process wizards tab which contains the SharePoint 2013 process wizard
 

Resolution

We suggested to install K2 for SharePoint 2013 on the client machine "Client Tool" and this managed to solve the issue.