How Do I get end effector coordinates from rigid body ?

firstly I'm trying to position control my 2-dof robotic arm ,it has a basic appearance because I'm learning the system right now.

I drawed in solidworks and i transformed into simulink multibody matlab.

İ need to get second axis end position coordinates or another robot's end effector same thing.

I searched some,and people says add transform sensor and i did.İ choosed position x y z output.but what will i give B and F as an input ? or from which one ?.