Was at home, some point during highschool, think school was out for some reason, don't really remember. Didn't really affect me much at the time (I'm in Florida, NY's on the other side of the country, so personal safety wasn't even a consideration). At worse, it felt kinda' like a natural disaster, or something along those lines. Had a cousin that was living within visual distance of the towers and another one that went up to help out with relief, but neither were hurt so there wasn't much concern. Sympathy went out to those affected, of course, but it was a very distant sensation.
Within a few years, we (The USA) had either caused directly or indirectly some substantial multiple of the number of deaths caused by the attack, ostensibly in retaliation to see justice done. Between that and realizing that terror attacks have done a helluva lot more damage to a number of other countries than it had in the 9/11 attack, I stopped really caring about the attack itself within a year or three. Blood price was paid, time to move on, other countries have it a lot worse, time to get off the soapbox.
That was years ago. I didn't even register it was the 11th of September until I saw this thread, and it's around 6:30 PM here. Actually had to look at the OP before I realized what the topic was.