Suppose you have this figure, and you wanted him to "see" one of 
the triangles.  You could take a red pen and mark over it as in
the second figure. If you don't want to mess up the original drawing,
you could get a transparent plastic sheet, place it on top of 
the paper, get a colored marker and trace the triangle that you wanted
to point out on the plastic sheet in red.  Or you could do as the third 
figure shows, redraw the triangle outside the figure the same shape 
and size of the triangle he is to "see". Eventually I think his eye 
will become trained so he can "see" the triangle.



Edwin