A pendulum is pulled sideways so that it is raised a vertical distance of 2 m above its resting position. Find the maximum speed the pendulum reaches after being released.

Same concept as before - the potential energy you apply in raising the object 2m is converted to KE as the object falls. The amount of work you put into the system is force x distance: here the force is the object's weight = mg. So you have:
PE = mgh (where h = 2 m)
Which gets converted to KE = 1/2 m v^2.

So:

PE = KE
mgh = 1/2mv^2

Note that the mass terms cancel out - in other woirds, you get the same answer regardless of the actual mass of the pendulum. Now you can solve for v.

How do I know the mass

As I said: you don't need to know the mass! It ciancels out of both sides of the equation.