1. Arboreal Survivor of 9/11 is Alive, and Well.

Question

(How do we read 9/11?)

2. One New York tree survived the 9-11 terrorist attack.
(How do we read 9-11?)

3. It stands today in the midst of the September 11 Memorial in lower Manhattan, strong and very much alive.
(How do we read 'the September 11'?)

4. You can see that this is prior to 9/11 and after it is the new growth, the smooth bark.
(How do we read 9/11?)

Answer 1

1 and 2 and 4 -- "nine eleven"

3 -- I'd put a "th" after "11" and say, "September eleventh."