Can you do a `which qmake` and if you get no answer do `echo $PATH`. That should show you where qmake is and the second command describes the path in your environment.

If you cannot find qmake those ways, you may need to do a `find / -name qmake` and if nothing shows up there, you may need to install it. Also, try `dpkg - l qmake` to see if dpkg knows about qmake.