This point is directly below the spinous process of the 5th lumbar vertebra (L5).
How to locate
Locate the Tufffier's line, which connects the two most superior points on the iliac crest. It generally intersects with the spinous process of the 4th lumbar vertebra (L4).
Then palpate in an inferior direction to the next vertebra (L5) and locate Ex-B-8 below the border of its spinous process, at the lumbosacral joint.