FYI, it can be stored in theoretically any key. But it's probably worth looking for SUFeedURL* at least.

  % plutil -p /Applications/iTerm.app/Contents/Info.plist| grep SUFeedURL
  "SUFeedURLForFinal" => "https://iterm2.com/appcasts/final.xml"
  "SUFeedURLForTesting" => "https://iterm2.com/appcasts/testing3.xml"