As Valerie has described, you can utilize Embedded Components for this.
Its still not 100% clear to me whether your PDE solutions are previously computed as plots (in the same Maple session) or as saved external image files.
You can have one Plot Component with some "action" code that discerns where you clicked (or the nearest point on a curve to the click point, etc). So then you have, programmatically, [xi,S(xi)].
You can have another Embedded Component for displaying the assciated PDE solutions. If the PDE solutions are actual Maple plots in the session (previously computed, or computed on the fly) then you could utilize a second Plot Component to show them. If the PDE solutions are external image files then you could utilize a Label Component to render them.
The "action" code of the first Plot Component could also programmatically put the associated PDE solution into the second component (whichever was suitable).
It's difficult to provide fuller details without having the actual full example at hand.