Hey Autocad for Mac Forum,
Solved my own problem!
HAVE TO ORIENT THE UCS SO THAT YOU ARE ON THE XY PLANE!
See attached photos.
First, select the UCS icon within the viewport on the layout.
Then click on the square at the intersection on the UCS icon.
Then select "move origin only".
then align so that the xy plane is on the plane you want.
Then when using the dimension tool, your dimension will show.
...Paul