From the interface: right-click on a 3D figure > Get coordinates, then click on the cortex:
https://neuroimage.usc.edu/brainstorm/Tutorials/ExploreAnatomy#Get_coordinates
From a script, you can find existing posts about this on the forum. For example:
Note that the ROIs defined in the Brodmann atlas from FreeSurfer are not suited for functional analysis, especially the motor and somatosensory regions. They are too inhomogeneous spatially.