SPSS unfortunately will not combine different geometric elements like that in the legend. For your example graph on the left what I would do is suppress the line and only display the shape and outline color in the legend. It is redundant with the color of the line so should be obvious. See the GUIDE: legend
statements in the inline GPL on how to do this.
DATA LIST FREE / X Y Group.
BEGIN DATA
1 0 1
2 0 1
3 0 1
1 1 2
2 1 2
3 1 2
1 2 3
2 2 3
3 2 3
END DATA.
FORMATS X Y Group (F1.0).
GGRAPH
/GRAPHDATASET NAME="graphdataset" VARIABLES=X Y Group
/GRAPHSPEC SOURCE=INLINE.
BEGIN GPL
SOURCE: s=userSource(id("graphdataset"))
DATA: X=col(source(s), name("X"))
DATA: Y=col(source(s), name("Y"))
DATA: Group=col(source(s), name("Group"), unit.category())
GUIDE: axis(dim(1), label("X"), delta(1))
GUIDE: axis(dim(2), label("Y"), delta(1))
GUIDE: legend(aesthetic(aesthetic.color.interior), null())
GUIDE: legend(aesthetic(aesthetic.color.exterior), label("Group"))
SCALE: linear(dim(2), min(-0.25))
ELEMENT: line(position(X*Y), color.interior(Group), missing.wings())
ELEMENT: point(position(X*Y), color.exterior(Group), shape(Group), size(size."14"))
END GPL.
And here is the graph and legend produced with my default chart template.