All the videos below come courtesy of LE55SONS YouTube channel. Take a peek into its contents to find more professional disassembly and repair vids.
There is also another video with instructions for replacement of Nokia N9's AMOLED display, Digitizer and Proximity sensor.
Here's a link to official Nokia N9 service manual id pdf, explaining you how to repair and replace particular components of the phone. Browse through its contents to find detailed instructions for disassembly of the phone. This might be a great supplement to the LE55ONS videos linked above.
Note: Mind that any home repairs lead void Nokia limited guarantee agreement. I do not take any responsibility for the damage and/or loss of guarantee resulting from following the above instructions.