(1) If you know the name of the program

Try on the command line:

find /usr -name 'evince'

Most programs are in the /usr/bin directory.

Then you can type on the command line:

/usr/bin/evince

This will start the evince program.

To know the hierarchy of the Linux filesystem (what is where) you can check the page about the Linux Filesystem Hierarchy on The Linux Documentation Project site

(2) If you don't know the name of the program.

Step 1: Open a terminal and list all running processes with their PID - process identifier number:

ps -e 

Step 2: Start your program

Step 3: Switch to the terminal and type again:

ps -e 

Step 4: Trial and error to find the process of your program.

Ubuntuone-syncd is in both lists with PID 2911. Ps is the process of the ps⁻command in the terminal. There are three possibilities left:update-notifier, aptd and evince.

On the command line for those 3 possibilities

man name_of_the_process

or

info name_of_the_process

or

name_of_the_process -h 

Replace name_of_the_process by the real process name.

In this case if we type

evince -h 

we get:

So evince is the GNOME Document Viewer we were looking for.