If i output high through a pin what will be its voltage
You don't output a high. You set an OUTPUT pin HIGH. The voltage at that pin is the reference voltage for the board. For most boards, that is 5V. For others, it is 3.3V.
If the sensor is a digital sensor, it will make the pin HIGH or LOW. The exact voltage on the pin is irrelevant.
If the sensor is an analog sensor, the output from analogRead() will be a value between 0 and 1023 that corresponds to where the input voltage falls on the scale of 0 to ARef. Again, the exact voltage is irrelevant.