On Sunday morning, I'm doing a demo lesson of Ulpan La-Inyan in Raanana at Telfed (if you're thinking of attending, let us know!).
The Hebrew word for demonstration when speaking of demonstrating an item or service is הַדְגָּמָה (hahd-gah-MAH). The root is ד.ג.מ (d.g.m), which is the concept of sampling.
So I'm doing a שִעוּר הַדְגָּמָה (shee-OOR hahd-gah-MAH) - a demo lesson.
Don't confuse הדגמה with word for political demonstration - הַפְגָּנָה (hahf-gah-NAH).