A simple pendulum of length $l$ has maximum angular displacement $\displaystyle \theta .$ Then maximum kinetic energy of a bob of mass $m$ is

At point B, $v=0$ and $P.E$ is maximum.

At point A, $P.E= 0$ and $K.E$ is maximum.

Height of bob at B, $AP= l-lcos\theta= l(1-cos\theta)$

Thus $P.E= mgl(1-cos\theta)$

Applying conservation of energy at A and B, $K.E_m +0 = 0 + P.E$

$\implies K.E_m=mgl (1-cos\theta)$