I have been getting this error from several sources, the latest in installing a new Canon printer

richard@richard-Predator-G3120:~$ sudo add-apt-repository ppa:michael-gruz/canon
[sudo] password for richard: 
 
 More info: https://launchpad.net/~michael-gruz/+archive/ubuntu/canon
Press [ENTER] to continue or Ctrl-c to cancel adding it.

E: Type 'sudo' is not known on line 2 in source list /etc/apt/sources.list.d/signal-xenial.list
E: The list of sources could not be read.

You have to remove problematic sources list file by

sudo rm /etc/apt/sources.list.d/signal-xenial.list

Also please note that the mentioned PPA does not provide packages for actual Ubuntu versions, so you have to remove it using command

sudo add-apt-repository -r ppa:michael-gruz/canon

And add other PPA instead:

sudo add-apt-repository ppa:thierry-f/fork-michael-gruz

to install relevant driver package.