May I know how much is the taxi fare from University Hohai to Nanjing International Airport?

I presume you refer to the campus on Xikang Road. Well, the cab fare is CNY150 or a little more.

The distance between the two places is almost 50km. You can also go by subway which takes about 100min:
walk to Nanyi Ershi Caochangmen - line 4 to Gulou - line 1 to South Railway Station - line S1 to airport.