Hi Mike,
If you have installed the application with default settings, the installer program creates a /bin/PixInsight launcher script, so you can run PixInsight anywhere on your filesystem by just saying PixInsight. The installer also integrates PixInsight with any freedesktop-compatible desktop manager, such as Gnome or KDE, so you should have a PixInsight application entry in the Graphics category of your launcher menu. Unless Ubuntu 16.10 has changed in a weird nonstandard way, which I seriously doubt, this must work.
At any rate, you should have an /opt/PixInsight directory. You can always run the installer program again, without parameters to perform a new standard installation.
A completely different problem is that if you have performed a clean Ubuntu 16.10 installation, then your system lacks a couple of required dependencies. See
this thread for an easy solution to this issue.