Almost all furniture and woodwork finished between the 1820s and 1920s was finished with shellac. But if you want to test to be sure, here’s the way to do it.
Put a little denatured alcohol on your finger and dab it onto an inconspicuous area of the finish, as shown in the accompanying picture. If the surface gets sticky or if the finish comes off on your finger, the finish is shellac. Shellac dissolves in alcohol, so you could use the alcohol to strip the finish if that is your intention, instead of using paint stripper