/usr/bin/assistant-qt4 is in qt4-dev-tools 4:4.8.7+dfsg-5ubuntu2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/bin/../lib/x86_64-linux-gnu/qt4/bin/assistant
/usr/bin/../lib/x86_64-linux-gnu/qt4/bin/assistant