it is safe to drive my1994 nissan maxima with the comfort button on in the city and does the comfort button activates the air shocks?

Based on this info., I don't think it matters whether it's city or highway driving, just personal preference: The power/comfort switch determines when your car shifts gears, Power makes it shift at roughly 4500 rpm, in the middle is around 4000, and comfort is about 3500. If you set it on power, you can accelerate more quickly, comfort makes the shifts much more comfortable and less jerky. Keep it on power all the time, I'd say, unless the shifts really bother you.. for two reasons: One it makes your car quicker which is always good, and secondly it improves gas mileage a bit.

RacerX is right, and the other part of you question is no, it has nothing to do with air shocks.