gdk:app-launch-context-set-desktop (context desktop)

context -- a gdk:app-launch-context object
desktop -- an integer with the number of a workspace, or -1

Sets the workspace on which applications will be launched when using this context when running under a window manager that supports multiple workspaces, as described in the Extended Window Manager Hints. When the workspace is not specified or the desktop argument is set to -1, it is up to the window manager to pick one, typically it will be the current workspace.