Are you asking how to turn off such line truncation? If so, the answer is M-x toggle-truncate-lines.
You can also set variable truncate-lines to nil in any given buffer. And you can set its default, global value using setq-default.
See the Emacs manual, node Line Truncation.
See also user option truncate-partial-width-windows.
You could discover this ...
In Spacemacs this functionality is easily toggled using SPC t f.
I'm not sure exactly how it is implemented but Spacemacs seems to use the fill-column-indicator package (defined in the .emacs.d/layers/+source-control/git/packages.el file).
Spacemacs also implements company and avy, I'm not sure if the fill-column-indicator breaks anything there.