The whole world knows about 9/11, unless they are unconnected people are aware it happened.
America is Japan's most important ally. So 9/11 is known but it's not on the publics mind like it is in America. 3/11 (The Earthquake and Tsunami) were bigger anniversaries... but my perception might be slanted as I moved to Fukushima after the disaster (don't worry, I don't have extra legs nor do I glow at night). I can go in depth my experiences living there if you guys are interested, but later. Tokyo Sarin Gas attacks get a lot of coverage too, but again that had a direct effect on people here. Anyhow, I need to sleep now!