Hello RSchnell,
Thank you for your fast response. Appreciate all your help and instructions.
For 1), the input pulse voltage due to function generator has increased.
For 2), I am using the differential probe across VOA&GNDA currently for the ground isolation. I am not moving to 3) yet since I found the connection question about the GND1, system ground DISABLE pin. I am getting different signals by different ground setup. Please check the pics below. 
I don't understand why the setup3 (only J2-2 connecting to system ground) is seeing a pulse response although the signal is not perfect yet. I personally think the setup1 and setup2 should be the correct way. Please help to clarify how to keep DISABLE pin low. In addition, is it a good way to use differential probe across C6 (TP3 vs. GNDA) for checking the output of ADuM3223?
Thank you so much for your help.
Linda