The "KN" is on the left hand side of the graph. The Displacement, is on the base of the graph.
You then have a series of curves all plotted at various 'angles'.
Select the displacement of the vessel, then draw a straight perpendicular from the displacement. Where this vertical line crosses the curves of angles, note the angle, and then note the value of KN.
First thought, you need to be sure that KN, is from the baseline/keel of the boat to the metacentre. (not all produced like this).
Then once you ahve the KN data you do the following:
GZ = KN - KG x sin (angle)
KN = cross curve ordinate
KG = centre of gravity above datum (Same datum as KN, corrected for free surface effects)
angle = heel angle, from cross curves
So, you draw up a table of the items you have
Angle, going down, and going across you have columns of
Angle, KN, sin (angle), KG x sin(angle), GZ.