According to the package description this package provides support for
systemd journal:

“
 This is a full conky with most compile options enabled:
 .
 Wayland, X11, XDamage, XDBE, Xft, MPD, MOC, math, hddtemp, portmon, RSS,
 Weather, wireless, IBM, nvidia, eve-online, Imlib2,
 apcupsd, I/O stats, argb, Lua and the cairo and imlib2 Lua bindings,
 Audacious, PulseAudio, iCal, iconv, IRC, and systemd journal.
”

Also the manpage lists “journal” as a known variable:

“
       journal lines (type)
              Displays  last N lines of the systemd journal.  The optional type can be `user' or `system' which will show only the user or system journal respectively.  By
              default, all journal lines visible to the user are shown.  A maximum of 200 lines can be displayed, or until the text buffer is filled.
”

However, using this variable in the config file leads to the message

“conky: unknown variable '$journal'”

and conky itself displays the text

“${journal}”