Hello Ram,
The DE0-Nano is supplied with a golden reference design.
If I am not mistaken, I2C is used in this design to manage the video part.
On the other hand, what you are trying to do is not so easy. Have you considered to start with a test application in VHDL / Verilog without a processor, and then go further with nios & the SOC that is on the board?
I2C signals can be generated with an FPGA using a state machine, in the beginning not using IP but writing your own blocks can help a lot in debugging and understanding what is going on.
Best Regards,
Johi.