Please give me an example how to insert the "show all" into a link.
This would be most helpful.

Thanks

Like this: <a href="http://rpol.net/display.cgi?gi=134&ti=6225&date=1439040284&msgpage=&show=all">Link</a>

You can use the "All" link at the top right of any thread which goes over one page, then just copy the URL from the address bar, as that will automatically include the "&show=all" part in the link.
This message was last edited by the user at 15:34, Sun 23 Aug 2015.

Sounds good.

Would I be able to combine the "show all" with the use of the Anchor tags points?
This message was last edited by the user at 15:30, Sun 23 Aug 2015.

I find the easiest way is to right-click on the [all] link at the top right of the thread and choose copy link/copy shortcut.

Yes you can combine it with anchors.  Every message already has an anchor (#1 onwards).  The user created anchors are actually designed for linking within the character sheet/description or post, but you may mix'n'match.