If called without arguments, it looks for modules in the gdk-pixbuf loader directory.
If called with arguments, it looks for the specified modules. The arguments may be absolute or relative paths.
Normally, the output of gdk-pixbuf-queryloaders is written to libdir/gdk-pixbuf-2.0/2.10.0/loaders.cache, where gdk-pixbuf looks for it by default. If it is written to some other location, the environment variable GDK_PIXBUF_MODULE_FILE can be set to point gdk-pixbuf at the file.
The environment variable GDK_PIXBUF_MODULEDIR can be used to specify a different loader directory. The default gdk-pixbuf loader directory is libdir/gdk-pixbuf-2.0/version/loaders.