I believe that I have the answer to the question as the source appears to be very reliable; a person who claims to be the “former Senior Constable at NSW Police Force (2002-2011)”. He or she writes on the Quora.com website and their answer is:
7 dogs died as a result of the 9/11 attacks. 5 were homeless, 1 was a puppy taken to work and 1 was a police dog.
There are other answers to the question on the same website but none so positive and confident. One person says that a dog was heard to be calling in “an underground PA holding facility blocked by rubble” but the cries were ignored as rescue teams were searching for people. “PA” stands for Port Authority as I understand it.
Ten years ago Elisa, a colleague of mine wrote about the cats of 9/11. You might like to read it.