Adam Cohen talks about marking 10 years since Leonard Cohen’s death with a Toronto tribute featuring Feist, Rufus Wainwright and Serena Ryder. Adam, an accomplished recording artist in his own right, is taking the family-produced show across Europe next year — Jan. 15 in Warsaw — and has already performed in Quebec City and his dad’s hometown of Montreal this past week, but tonight’s show is “the most important date,” he tells.