Difficult to say without seeing the vehicle first hand, but it does sound like a broken crank to me. There's a misfire along with the knocking noise, which points to a crank failure.
With the engine off, and the key in your pocket, try putting a spanner on the crank pulley nut, and give the crank an rock back and forth in an anticlockwise and clockwise direction to see if there's any slop. My guess is you might feel a few degrees of looseness, which would show a broken crank.
If there's no looseness, then look around the crank pulley for silvery flecks of metal, which means the pulley has de-laminated, and is hitting the engine block.
However this issue doesn't cause a misfire, which this engine has.