Variables are saved in the
variables table in the database. Every module can define its own variables. It is mostly common that the core and contributed modules save their configuration/settings as variables.
It is also mostly common that the modules add a prefix to their variables, so that you can look at the
variables table in your database and search for the related module if they defined any variables.
Another approach would be looking in the source code of the configuration form for the related field. For example for
file_temporary_path, you would see:
<input type="text" class="form-text" maxlength="255" size="60" value="/tmp"
Here is the
name attribute hints that this configuration field will be saved in
Moreover, if you have Devel module installed, there is a Variable Editor under the path
devel/variable, which lists all the variables defined in your site and gives you the possibility to edit or delete them.