Wifi Not Working Ubuntu 18.04 Troubleshooting Guide

Installing Driver

3. 3. Installing Wifi Driver

   How to Install Wireless Driver in Ubuntu

   Wifi Driver Ubuntu Setup Guide

   GNU/Linux Ubuntu Wifi Driver Installation Tutorial

   And then in case of further Trouble you should also try to see: How to Update Firmware Guide.
   Last, you have to know how a Possible Turn around is of Buying some Cheap USB Wireless Dongle.