I don’t know if I understood correctly, but I did some tests.
$ gmic e \$\{-path_cache\}
[gmic]-0./ Start G'MIC interpreter.
[gmic]-0./ /home/fabio/.cache/gmic/
[gmic]-0./ End G'MIC interpreter.
$ gmic e \$\{-path_gimp\}
[gmic]-0./ Start G'MIC interpreter.
[gmic]-0./ /home/fabio/.config/GIMP/2.10/
[gmic]-0./ End G'MIC interpreter.
$ gmic input_cached gmic_denoise_cnn.gmz
[gmic]-0./ Start G'MIC interpreter.
[gmic]-0./ Input cached file 'gmic_denoise_cnn.gmz'.
[gmic] *** Error in ./ *** Command 'input_cached': Unknown filename 'gmic_denoise_cnn.gmz'.
$ cp /home/fabio/.cache/gmic/gmic_denoise_cnn.gmz /home/fabio/.config/GIMP/2.10/plug-ins/
$ gmic input_cached gmic_denoise_cnn.gmz
[gmic]-0./ Start G'MIC interpreter.
[gmic]-0./ Input cached file 'gmic_denoise_cnn.gmz'.
[gmic] *** Error in ./ *** Command 'input_cached': Unknown filename 'gmic_denoise_cnn.gmz'.
sudo cp /home/fabio/.cache/gmic/gmic_denoise_cnn.gmz /usr/lib/gimp/2.0/plug-ins/
$ gmic input_cached gmic_denoise_cnn.gmz
[gmic]-0./ Start G'MIC interpreter.
[gmic]-0./ Input cached file 'gmic_denoise_cnn.gmz'.
[gmic] *** Error in ./ *** Command 'input_cached': Unknown filename 'gmic_denoise_cnn.gmz'.
sudo cp /home/fabio/.cache/gmic/gmic_denoise_cnn.gmz /usr/share/gmic
$ gmic input_cached gmic_denoise_cnn.gmz
[gmic]-0./ Start G'MIC interpreter.
[gmic]-0./ Input cached file 'gmic_denoise_cnn.gmz'.
[gmic] *** Error in ./ *** Command 'input_cached': Unknown filename 'gmic_denoise_cnn.gmz'.
$ls /home/fabio/.config/GIMP/2.10/plug-ins/q*
ls: impossibile accedere a '/home/fabio/.config/GIMP/2.10/plug-ins/q*': File o directory non esistente
$ locate gmic_gimp_qt
/usr/lib64/gimp/2.0/plug-ins/gmic_gimp_qt
/usr/lib64/gimp/2.0/plug-ins/gmic_gimp_qt/gmic_gimp_qt
I hope I did right