should I put the folder were my current nam is ?
No. Just do 'sudo cp ext-nam /usr/local/bin/'. See post #2.
Nam and ext-nam are separate applications.
A specific nam version is not related to a specfic verson of ns2.
Any nam can be used together with all versions of ns-2.xx.
The prefered nam for all ns-2.xx : nam-1.14, because it's mostly static.
A "static" nam will work OK also on an OS with no ns2 or tcl,tk.
And the location of 'nam' should also be /usr/local/bin/.
Which is what you get with :
cd ns-allinone-2.35/nam-1.15/ && sudo make install