How do I meet someone who is arriv at terminal 3 and I at terminal 2 in Beijing airport to share transport to hotel?

You may meet in the restaurants in the airport to catch the car. There is StarBucks in T3 and they are at East side of Public Area, 4F, Close to Gate E10, International Waiting Area and East side of International Waiting Area, 2F, T3E and you can meet each other there.
Or in T2, the Starbucks are at Public Area, 1F, T2 and International Waitng Area, 2F, T2.