My MySQL-server stopped working last friday.

When trying to restart it via WHM i get the following error:

mysql has failed, please contact the sysadmin (result was "/usr/bin/mysqlshow: Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' (2)").

Have WHM 8.6.0 cPanel 8.7.0-R80, anyone know what to do??

try rebooting the server
if that dont work try upgrading your cpanel & whm to the stable 8.8.0