The sudo password is normally your regular password for nick.

if you have your SU password you can try this.

$ cd /downloads/fritzing-0.9.3b-linu-AMD64 (The location of the install_fritzing.sh file)
$ su
enter the passord for SU

./install_fritzing.sh

after it installed, type "exit" to leave the SU prompt. (w/o the ")