The show opened a week ago at the Galleria il Sotoportego at the Scuola Internazionale di Grafica, which is indeed located at Cannaregio 1798.
I already knew the postcard was confusing lots of people. My mother wrote of several friends who'd ended up going to the Frari to see the exhibit. Indeed, even worse, the day after postcards were dropped off at the Frari, the monks there called irately to find out why the Scuola had scheduled an exhibit there without asking! But what my mother was finding is that Italian-speakers were more likely to be confused than non-Italian speaking ones. She didn't have too much evidence either way on this subject, which is where the poll comes in.
As of a few minutes ago, eighty percent of the non-Italian speaking respondants to the poll would have gone to the correct venue, based on initial impressions, while sixty percent of respondants who know at least a bit of Italian, would have gone to the wrong venue. This supports my mother's hypothesis. It also shows that the basic layout of the postcard is fairly sensible, since the physical layout of the card helped most of the non-Italian speakers to find the correct information, even if the actual execution in practice left something to be desired. The actual success rate of people showing up at the right venue is likely to be higher in both cases than 80 and 40 percents respectively, since many of you would have double-checked before going; but not all. After all, if you know where the show is, why double-check?
The problem is that there is more than one place listed on the postcard. The church of Santa Maria Gloriosa dei Frari, more usually referred to just as "the Frari", is a fairly major landmark in Venice. Tourists who've been there a few days will generally have heard of it, and certainly anyone vaguely local knows it. No address is needed for such a major destination, in fact, which is why it wouldn't a problem that none is listed on the postcard - except, of course, that the exhibit isn't at the Frari.
As many of you correctly observed, the Sala Capitolare at the Frari is the show's subtitle. More specifically, it's the subtitle of the print which was used as the background to the postcard. (It's an engraving with lots of stippling, for all it looks rather like a watercolor when it's been reduced so much.) The image in the print, of a room with a series of columns, is the Sala Capitolare itself.
One last point on Venetian addresses. They aren't always as useful as they could be. The city is divided into sestieri, into sixths, each with its own neighborhood name. Cannaregio is one of those six. Addresses aren't done on a road-by-road basis, but throughout the sestiere. Addresses for each sestiere start at 1 and go up into the several thousands, but they don't generally do so with a great deal of order. Sure, parts of roads will be sequential for a little while, but it rarely lasts. Addresses do uniquely identify buildings, though. To use them, get a copy of Call, Campielli, e Canali, a book-length map of Venice, and look up the address in the index. Then spend several minutes scouring the resulting page in search of the number. Now you'll know where it is.
This is why just telling people that the exhibit will be in the Frari is a much easier form of giving directions than telling them to find an address. Except, of course, the exhibit isn't there.