While engine is idling, pull off 1 spark plug wire at a time, if knock quiets down then that cylinder has bad connecting rod/bearing.
Hydrolock:
When an engine is running and a piston can't continue its travel to the top of the cylinder, cylinder has water in it, the piston comes to a sudden stop, with the rotating weight of the rest of the cylinders and crank still pushing on it.
The softer parts(bearings) deform and harder parts can bend or break(connecting rod and piston).
Valves could be effected but when a cylinder hydrolocks valves are closed or it would just push the water out.
Connecting rod bearing knock
When bearing is deformed(or worn out) there is a gap between crank journal and connecting rod.
This gap causes a knock but only when it's cylinder fires.
When a piston is in motion up on its compression stroke the gap is at the bottom, as piston passes TDC the crank starts pulling it down, so gap moves to the top, then the spark plug fires and KNOCK, as the gap closes fast and the metal to metal slap noise is heard.
Removing the spark would quiet the knock, if it is a connecting rod issue