Customer's tax ID in GS

Hi,

this thread follows the previous one concerning invoicing from GS. Apart the creation of invoice with GS, there is still another problem I cannot solve. Where is customer’s tax ID displayed in the order of GS? There is a specific option in ebay preferences that force customers to provide their tax IDs, which is necessary for fiscal reasons. So where is this ID in GS? Is there a specific field that I cannot see?

Thanks again for any advice.

Federico