In a lot of ways shop floor printing can be considered a major project on its own. If your implementation has a printing infrastructure in place then I recommend leveraging that as much as possible. This may include having to develop custom actions or interfaces to other systems. Most industrial concerns will use printing and management software like those provided by Peak, Loftware, and Bartender. I am sure there are others.
So to address your questions. Being able to use the PCo interface to send a document to a printer would depend on the specific printer and it's capabilities. You would have to research manuals and developer guides provided by the manufacturer.
If you have a document you would like to print from the server you would have to interface with a print server or other mechanism provided by some software as mentioned above, interface with some other system like ECC that can do the actual printing, or possibly write a custom action to print to a printer connected to the MII server.
For printing on clients, unless you have developed a thick client the best you can do is push the document to the browser for the user to print.
Regards,
Christian