I am in the Army and getting ready to PCS to the Pentagon. What Army Post will I be assigned to?

Very likely your HQ assignment will be Fort Myers and you will be assigned to Headquarters and Headquarters Company, US Army. A great many of the people in the Pentagon including the CJCS when he is Army is assigned to that company. It will be meaningless to you as you will report to the Pentagon and only go to your company when you need paperwork done.