At what point/points the acceleration and velocity of a body executing simple harmonic motion have maximum and minimum values?

Oscillations occur when energy is swapping between two forms.

In SHM one of these is usually kinetic and the other is potential energy.

When the kinetic energy is a maximum the acceleration must be zero. ( because the speed cannot be either increasing or reducing at the maximum)

This condition occurs at the midpoints of the motion.

The acceleration is at the maximum when the speed is zero.

Which must occur at the extreme extents of the motion.