Network controller: Intel Corporation PRO/Wireless 3945ABG
That is it. Your WiFi requires proprietary software. Trisquel, by its nature, doesn't include proprietary software so your WiFi doesn't work.
Your options are to replace the WiFi card or to use a USB port for WiFi or go without WiFi.
This USB WiFi thingy will work just fine without any proprietary bits: https://www.thinkpenguin.com/gnu-linux/penguin-wireless-n-usb-adapter-gnu-linux-tpe-n150usb
