The old resolv.conf is now a symlink so you cannot edit.
Instead Pop (and Ubuntu) use systemd-resolve
You can view the current DNS setup by issuing:
sudo systemd-resolve --status
You can change the DNS server only per interface.
As such you can issue:
sudo systemd-resolve --set-dns=8.8.8.8 --interface=enp0s31f6
To change the DNS for Ethernet (look for your ethernet device using ifconfig).
You can flush all your local cashes using
sudo systemd-resolve --flush-caches.
You can test the DNS now:
dig www.ibm.com
Done.