The Rose theater is located at the corner of St. Marks Ave. and Vanderbilt St. ((I don't know what -really- existed there...I just nabbed the location for my own fictional purposes.)) It's just a few blocks from the elevated train (indicated by the red line) and fairly close to Prospect Park. ((Many thanks to the wonderful Verity for finding the maps!))

A closer view: Here The Rose is marked by the rose-colored square.