How to do I2C on Arduino with SDA and SCL pin already used i have a Arduino screwshield from sparkfun that I purchased: https://www.sparkfun.com/products/9729 which I used to put between my arduino uno and my 2.8" TFT LCD touch shield so that I am able to use the unused pins. I have to make an I2C connection between 2 Arduino Unos which I understand will require the A4 and A5 pins however the TFT currently uses both pins. also, my tft screen is from here: https://www.sgbotic.com/index.php?dispatch=products.view&amp;product_id=2756

The schematics of my tft are: http://www.sgbotic.com/products/datasheets/development/02756-schematic.jpg .

I am wondering if I can just use the A4 and A5 pins using the screw shield anyway since according to the schematics, the A4 pin is connected to the LCD_RST or is the pin necessary for displaying images taken from the SD card? 
If that isn't the way, how should I go about doing it, does anyone know?
No, you can't just use it. While I2C itself may work, the screen will keep resetting itself all the time and will be useless.

You may be able to get some luck with a software bit-banged I2C  on other pins. However I would personally choose to modify the TFT screen's PCB and cut the LCD_RST signal from the A4 pin and connect a 10kΩ resistor to +5V, or re-route it to another pin. That way you can then use I2C.