"He ... designed stage sets, theatre costumes and posters, including a signed one around 1920 for his father-in-law's Europäische Güter- und Reisegepäck-Versicherungs-AG travel insurance firm and examples for Munich's Deutsches Theater."
From this, I gather that Schnackenberg had few financial worries during his productive years. The extent of those years is obscure to me, being based on the examples of his work found on Internet image searches. The poster images I downloaded seem to range from 1910, or perhaps a few years before, into the early 1930s.
Other biographical sources on the Web are equally sparse regarding him -- especially his career after the early '30s, aside from one remarking that he "worked" in the town where he died. Some photographic evidence suggests that he was making paintings rather than posters by then.
As for his style, it was more "arty" or "mannered" than the work of Ludwig Hohlwien, Munich's most famous poster artist. I find his posters more interesting than likable, but you are free to disagree.