I was able to fetch the dex param from the interface. I tested with UR5 and the threshold mentioned here is correct. In case someone needs a sample code for this, @ajp already posted a sample code for it as he mentioned.
I was able to compute the dexterity with the information from @malacasse but with a 0.00002 difference from the actual dexterity reported by the robot. I think I will be able to use this to avoid singularity in my grasp planner.
Thanks a lot again, for the quick and informative replies!