Don't have time to try to look up specifics, but I'd guess that the smallest venue on the current list of tourdates would probably be somewhere in the US, since DT typically plays to smaller audiences there than in Europe. And I'd imagine that it would probably be one of the (relatively) smaller cities instead of one of the big metropolitan locations. So I'd imagine that it is probably one of the following:
Albany, NY
Cincinnati, OH
Royal Oak, MI
Portland, OR
Seattle, WA