u/Crusheded

Posting in case it helps someone else.

Signing into myprint.unibocconi.it you use your regular student ID and password (that you use for all other uni websites).

When you walk up to a Bocconi printer, the touchscreen asks you for a User ID.

This is NOT: your student ID, nor is it the myPrint ID (alphanumeric code on the myprint site)

What it actually wants is an 8-digit number called your "primary pincode personale" / "personal primary pincode".

It was emailed to you by myprint@unibocconi.it

The code is not displayed anywhere on the myPrint website.
If you've ever reset your pincode, the current one will be in a more recent email, and that email sometimes doesn't show up right away

Hope this saves someone the headache.