I2C standard specifies two separate lines for Input/Output. You will want to have two separate external pins to get it to work. There are chips that communicate over 1 pin, but it is not I2C standard.
If you really need to reduce the pin usage to one wire, something like this: https://datasheets.maximintegrated.com/en/ds/DS28E17.pdf
would be your best bet.
thanks for your answer. My question was not clear enough.
It is clear to me that I will need a SCL and a SDA per I2C.
The question was about how to use the same pin as input and output.
What was not clear to me is how I can use ONE pin simultaneously as input and output.
Up to now I have always uses control registers and status registers connected to pins.
I think it is not possible to connect one pin to a control register AND to a status register.
Now I found out that I can use a bidirectional pin and use the API of the pin directly
without status or control register - certainly 2 bidirectional pins for each I2C.
You can runtime-modify the drive mode of the pins to support Input/Output. Thus, you can switch and use a single pin as both input/output by changing the mode and settings during runtime based on your current directional support.
The datasheet/documentation within PSoC Creator IDE for the Pin Component should have all the information you need to set the input/output modes of the pin at runtime.
Just configure the drive mode using software when you want to switch the mode. (High-z for input, strong drive or pull up/down for output).