Hello @Abbas,
As Microsoft is moving to cloud k2 is also decoupling from SharePoint, which is a good thing but, on the other hand, K2 had to cut down some of the SharePoint integration features as well. K2 has less footprint in SharePoint 2013 and now use rest API to communicate with SharePoint. In this case, I think you won't be able to find anything with PowerShell.
I am not sure how you have integrated workflows with k2. You might be able to trace out the lists with K2 workflows, in case they are SPWI-based processes. Which includes those created in K2 Studio or Visual Studio that utilize the SharePoint Events Process, SharePoint Workflow Integration Process Wizard or the SharePoint Workflow Integration Client Event. Also included are K2 Designer for SharePoint workflows for lists and libraries. SPWI-based processes does not Sharepoint 2013
below articles will give you the big picture.
https://help.k2.com/kb001614
https://help.k2.com/displaycontent.aspx?id=5782
Tip - Check out the K2 database, you may find somewhere.