How do you read the differential mark?
Formally, The derivative of...
Y equals the sine of f-of-x, implies that the derivative of y equals cos f-of-x times the derivative of f of x.
Informally, and depending on dialect, you can say either 'prime' (as per Humbulani's answer) or 'dash' - f prime of x, y-dash etc. The former is predominant in (but is not restricted to) the US, while the latter is relatively common in the wider Anglosphere.
Refer to: How do you pronounce the symbol ' in f'? and What is the practical difference between a differential and a derivative? for further information.
If x is a distance, ẋ can also be read as the x component of the velocity.
If x is a distance, and is also the only direction of motion, ẋ can also be read as speed or velocity.
If x is a distance, ẍ can also be read as the x component of the acceleration. If x is a distance, and is also the only direction of motion, ẍ can also be read as acceleration.