Where can I find a fax machine for public use in Poznan?

This is a ridiculous question, but where is there a fax machine for the public to use in Poznan? The printing store on Glogowska and the post office do not have one anymore.

Try one of the nicer hotels near the conference centre. They usually have a hotel 'business centre' where you can fax for a fee, assuming they haven't stopped with faxes too.

Alternatively, scan and email?

If that's not what you need, try:
wirtualnyfaks.pl
or
tanifax.pl
or
e-fax.pl

Or Google 'popfax' for something similar in English.