I have seen a closed ticket from 2006 saying that is not possible.
Maybe be possible now ?
It would be really really nice to have this capability
Thanks for all your great work
No, it is not possible. Gnuplot does not cache settings of previous plots.
Everything is possible. But some things require more drastic changes than others. No one has stepped up to implement mouse tracking or zooming in multiplots. It would require separate coding for each terminal type. Some would be easier than others.
Petr: While it is true that the core gnuplot code does not retain information about previous plots, many (all?) of the interactive terminals retain a private copy. I know this is true for the x11, svg, and canvas terminals, and I think it is true for qt and wxt also. The missing piece is to also keep bounding-box information about which rectangle on the screen contains which plot. That tracking would need to be added to the core code first, but after that it is a question of finding someone interested in writing the support code for each terminal.
Mouse tracking can be relatively easy (every viewport remembers its mousing info).
Otherwise, it depends what do you use multiplot for and what mousing for. If it is an interactive work, than you can use multiple terminals or multiple gnuplot instances and thus you don't need mousing in multiplot.