Comment 8 for bug 1251178

Because this is top post being shown in Google search for problems with qdbusviewer and they persist also on 18.04 here is the solution:

1. Find an error message. In my case (even after installing default):

    qdbusviewer: could not exec '/usr/lib/qt5/bin/qdbusviewer': No such file or directory

2. Find in which package is file being reported as missing:

    $ apt-file search /usr/lib/qt5/bin/qdbusviewer
    qttools5-dev-tools: /usr/lib/qt5/bin/qdbusviewer

3. Install found package:

   $ sudo apt install qttools5-dev-tools

Voila!