Quite generally, you might want to see this thread.
More specifically, the smart rules are here: /Users/yourusername/Library/Application Support/DEVONthink 3/SmartRules.plist; if you copy that file from the old to the new Mac, the smart rules will be available in your new installation of DT.
Smart rules are not synced; there is a certain logic to this (think teams syncing databases, but each team member has a different assignment and thus different requirements with regard to smart rules & groups), although I do wish syncing this additional data was optional.