GtkLabel::get_layout_offsets

Obtains the coordinates where the label will draw the PangoLayout representing the text in the label; useful to convert mouse events into coordinates inside the PangoLayout, e.g. to take some action if some part of the label is clicked.

Of course you will need to create a GtkEventBox to receive the events, and pack the label inside it, since labels are a Gtk::NO_WINDOW widget. Remember when using the PangoLayout functions you need to convert to and from pixels using Pango::PIXELS or PANGO_SCALE.