I`m trying to make SharePoint Workflow which will automatically create Document Library on Subsite with name "Library for [item name]", where item name is title of just created item. Is it possible via SharePoint Workflow or not?
It's possible via workflow, but there's an easiest way. You could simply implement an item event receiver which detects when an item is added and creates a document library.
You can refer to this link ( https://msdn.microsoft.com/en-us/library/ee231563.aspx) to better understand how to implement the item event receiver.