"pkd" process on El Capitan
Solution 1:
The manpage says:
NAME
pkd -- management and supervision daemon for plug-in services
SYNOPSIS
pkd [-v]
DESCRIPTION
pkd manages plug-ins for the PlugInKit subsystem. It is a classic launch
agent managed by launchd.
Sounds pretty safe to kill it off, by opening a terminal and running:
launchctl stop com.apple.pluginkit.pkd
It should restart itself whenever it's required (possibly immediately).