The highest vertical position is where your maximum potential energy lies. At the highest altitude point of course ! This is when the kinetic energy is only due to horizontal motion (since the vertical component reaches zero).
Objects in free fall, disregarding terminal velocity, accelerate at 9.8(m/s)/s. so for every second it was falling, it gained 9.8m/s in speed. 9.8 * 10 = 98m/s
