Hi,
It cannot/shouldn't happen completely automatic as a graph can contain many plots from various datasets.
Although there should be various ways to make it be more sophisticated, a simple way is to run the following
1-line script, for example from the "Custom Routine Button" to show the active dataset in the
graph's longname:if(exist(%H)==3) page.label$=%c;
http://www.originlab.com/doc/LabTalk/guide/Getting-Started-with-LT#Custom_RoutineCustom_Routine_Button
Hope this helps.
--Hideo Fujii
OriginLab