The formula for kinetic energy is E(k)=0.5mv^2
Since projectiles have two velocity components (horizontal and vertical), I’ll answer your question with regards to both.
So basically, at its maximum height, the kinetic energy of a projectile is equal to the amount of kinetic energy calculated with the horizontal velocity, because a projectile still moves horizontally if it’s at rest vertically.
So,kinetice energy is maximum at range R