Having heard this read only in Korean, I don’t know how to read it in English. What is the right English reading?
It would normally be read aloud as:
f of x equals x squared
There are some variations you might hear. For example, sometimes is is used in place of equals.
If the exponent was 3, you would say cubed. Anything higher than three (say, for example, 5) would generally be read aloud as:
f of x is x to the fifth (power)
f of x is x to the power of five
f(x)=x2 is simply read as f of x equals x squared. f being the function name and x being the input and x2 serves as the output. https://www.mathsisfun.com/sets/function.html