If you used a dipole fitting or dipole scanning procedure, you just have to click on a dipole to get its coordinates:
https://neuroimage.usc.edu/brainstorm/Tutorials/TutDipScan#Displaying_dipoles
If you are using distributed source models, you can get coordinates of any point on the cortex surface with the popup menu "Get coordinates":
https://neuroimage.usc.edu/brainstorm/Tutorials/ExploreAnatomy?highlight=(Get+coordinates)#Get_coordinates