What is notation for the Second Derivative?
If you prefer Leibniz notation, second derivative is denoted
If you like the primes notation, then second derivative is denoted with two prime marks, as opposed to the one mark with first derivatives:
Similarly, if the function is in function notation:
Most people are familiar with both notations, so it doesn't usually matter which notation you choose, so long as people can understand what you're writing. I myself prefer the Leibniz notation, because otherwise I tend to confuse the apostrophes with exponents of one or eleven. Though the primes notation is more shorthand and quicker to write, so many people prefer it.