Hi!
I assume you have some real 3D features in your DWG and want to annotate slope between two objects (In a plan).
You should use the radio button according to wanted value, in your case it should be slope.
Toggle the button Z of so it is on (you are snapping from and to real 3D objects with elevation). Toggle also of the last button in the second line if you dont want direction arrows.
Finally press the button with a arrow and the letter A (Annotate)
In the menu Settings you'll find settings for text height, prefix etc.
If you are planning to triangulate a surface you can easily annotate slope at any point on the surface.