How do I send data to raspberry pi connected over wifi from arduino connected to a laptop which is in turn connected to the same wifi network as raspberry pi?
What is it that you want to send ? If it is just sending some files, Raspberry Pi can be set-up as as
ssh server and you connect to it from your laptop with a
ssh client. See here for more on Raspberry Pi
If you are looking to send data in a client-server fashion, then obviously, a server should be running on the Pi and the appropriate client on the laptop and the data transformation for the application layer protocol.
As cogitoergosum says, you can connect the laptop to the raspberry pi over ssh, and you can connect the raspberry pi to the laptop with serial commands.
You can then use Processing to connect the arduino and the wifi together on the laptop.
If you want to remove the overhead of the laptop to remove it sometime, look in to the X-Bee shields. There is a wifi one there but they can be costly.