What are you trying to do? I assume join the wing half to the other with the center on the table? The place they would be talking about then would be the center of the Leading edge of the wing at the tip. Right where the top rolls around and becomes the bottom on the front of the wing at the tip. I am not at a system I can draw it. Sorry.

Other words, on the tip, draw a line from the center of the leading edge to the center of the trailing edge. That is where they want you to measure the dihedral.