I will arrive NJ airport 3.30 pm. Which bus or train to Nanjing Expo Hotel ?

No direct bus or train can take you there directly! I suggest you take airport shuttle bus line 2 to Zhonghuamen metro station and then catch a taxi to your hotel. Or upon arrival at Zhonghuamen station, take local subway line 1 to get off at Yuantong Station. Then your hotel will be around 1.5km away!