It took me a while to figure this out. I use Home Manager to manage my Gnome settings by setting dconf.settings = { ... }. My settings are non-trivial (for example my paperwm module). So it's helpful for me to check the actual dconf settings that Home Manager produces.
To do that build your configuration with home-manager build, open result/activate, and find a line that looks like this:
$DRY_RUN_CMD $DCONF_DBUS_RUN_SESSION /nix/store/4ab7dx08wx640444m71axlqvbrvz73bv-dconf-0.40.0/bin/dconf load /
< /nix/store/0hdnvwx8d9sifd6ib8n2hhblyblq0ccp-hm-dconf.ini
The store path for hm-dconf.ini has the settings.
Edit: added a line break to the script line so you can see the relevant store path