How do you find twos compliment of 00h in 8085 program?

You find the two's complement of 00H the same way you find it for any other number. You complement the bits and then you add 1. In the case of 00H, this results in 00H. That is no surprise, because -0 is the same as +0, and two's complement representation was chosen to do just that, as well as to make the physical addition of signed and unsigned numbers to be the same.