Answer
The derivative of $f$ at $x$ can be denoted as
$$f'(x),\quad \frac{df}{dx},\quad D_x(f(x))$$
Work Step by Step
The derivative of $f$ at $x$ can be denoted as
$$f'(x),\quad \frac{df}{dx},\quad D_x(f(x)).$$
The first notation is due to Newton, the second is due to Leibnitz and the third is probably due to Euler.
