Hey, that thing is gorgeous! Its Nno toxic, environment-triendly, Sare and dorless! 
Also it is moisture proof and waterproof, but don't clean it with water or a damp cloth, it may break!
And don't forget to not make strong striking on it. Not-so-strong striking is ok.

That's standard
Chinglish, I've grown used to it by now so it's barely amusing (Well, except for
this photo from a hospital in China which had me laughing out loud).
What a pile of crap. Dispose of this thing, the best it will do is light up your friends house.
Unfortunately, it is not mine to dispose of.
That's a bad idea. The oscilloscope will float at the mains voltage and could give you a nasty shock, if you touched it.
How about placing a microphone and amplifier near the piezo and looking at the waveform with the oscilloscope? That's much safer and will actually show you the sound wave being produced, rather than the electrical signal to the traducer, which might not match it perfectly.
Thanks again Zero999, I took your suggestion and tried to connect an electret microphone to my scope but I struggled to get a clean signal. Nevertheless, even with a "dirty" output you make out enough:

It looks like the signal is occurring every 5 divisions, so, exactly 100Hz (2ms per division), but the signal isn't clear enough to differentiate 1 cycle of the resonant frequency, even though 0.25 of a division (2KHz) seems about right.