Table fields in webservice

I have an invoice, I assign invoice items to a table, I also have a webservice with a parameter of the DataTable type, but I don't know how to pass the table from docuware to webservice as a parameter?

Can the table type field be used in a workflow and passed as a parameter to webservice?

That is probably not possible.

You may be aware the workflow extension webservices work over the SOAP-Protocol, so data is exchanged as xml. That means it has to be serialized. 
While serializing the data in the table is generally thinkable, it is hard to generalise this because you don't know how long your table is.

I like to pass the fileCabinetGuid and the DocId to the webservice then connect to the Filecabinet from the webservice and retrieve all the index data I need.