If you have wmctrl installed, the first line of output from command
will show you the name of the window manager. If you don't have wmctrl installed, use the following command to install it:
sudo apt-get install wmctrl
Note, man wmctrl (that is, the man page for wmctrl) says in part:
-m Display information about the window manager ...
On my Ubuntu 11.10 / Linux 3.0.0-14-generic #23-Ubuntu x86_64 / metacity 2.34.1 system, the first line of output from wmctrl -m was: Name: Metacity
while echo $DESKTOP_SESSION showed ubuntu-2d and echo $XDG_CURRENT_DESKTOP showed Unity.
On a fresh Ubuntu 15.10 install of Ubuntu desktop software on an old laptop, the first line of output from wmctrl -m was: Name: Compiz
while the DESKTOP_SESSION and XDG_CURRENT_DESKTOP values were ubuntu and Unity
Try find ~/ -type f -name "postgis-2.0.0" instead.
Using . will only search the current directory. ~/ will search your entire home directory (likely where you downloaded it to). If you used wget as root, its possible it could be somewhere else so you could use / to search the whole filesystem.