I am using openSUSE Leap 15.0 with KDE.
Gnucash is not able to locate and open the guide file despite the gnucash-docs
package is correctly installed.
I tried to dig a bit deeper with this invocation:

gnucash --debug --extra --log gnc.gui=debug

This is the relevant part of the trace file:
[...]
* 10:00:08 DEBUG <gnc.gui> [enter
../gnucash/gnome-utils/gnc-file.c:gnc_post_file_open()] filename 
* 10:00:14 DEBUG <gnc.gui>     [gnc_gnome_help] Attempting to opening help uri
ghelp:gnucash-guide
* 10:00:16  CRIT <gnc.gui>     [gnc_gnome_help()] La posizione specificata non
� supportata
[...]

Last trace is the italian translation for "The specified position is not
supported".

In my system the gnucash configuration file /.gnucash/config.auto is not
present despite it is mentioned in gnucash man help file.