Hi Kevin, Welcome to the forum,
Understanding the deeper level behaviour of piezo-electric materials gets into some advanced physics quite quickly, I won’t pretend to understand them fully.
I would expect this piezo element to typically output on the order of 10s or 100s of millivolts.
I’ve found some more information on piezo electrics and FAQs Piezoelectric Basics - Piezo Support
This piezo element is the 7BB-20-6L0 I’ve highlighted it’s entry in the datasheet below.
