I'm trying to use Rakarrack with a Jack aware sound editor.
I had hoped to use Audacity but it does not appear in Jack's
connections, so I guess it's not Jack aware.
Is there another sound editor that I can use to record
through Rakarrack into the sound editor ?

Audacity is jack-aware if you compile it with jack installed (and jackd is running). You may try recompiling audacity.

Just to be clear, by compile you mean config, make, make install from source ?
Or just removepkg and installpkg while QjackCtl runs ?

Uninstalling/reinstalling the package will not change anything -- jack functionality is only added to the package if jack is detected at compile-time (by which I do mean `./configure && make && make install` from source). I would encourage you to use the SlackBuild for Audacity from slackbuilds.org to compile and create a jack-aware Slackware package that you can then install. jackd does not have to be running when compiling but jack must be installed. After installing the jack-aware Audacity package jackd would need to be running to get the jack functionality at run-time.