How to draw TText in TH2F histogram being drawn with "S

I would like to add some text at certain positions in a canvas that shows a 2D histogram being drawn with “SURF”. The proplem is that I do not have the NDC coordinates of this specific data points where I would like to draw the text and as far as I found out, is there only the possibility to draw text in such a 3D plot by using NDC coordinates.
Any idea?

On simple way is to open the “toolbar” when you have the surface plotted. From the menu View/Toolbar. From there create a text interactively. You may have to create it on the side and then move it on top of the surface. Then safe the result in a .C file via the menu File/Save. You can then look at the generated macro and see what to do.