Usually, the best indicator is if the sound changes based on engine load. While crusing at various speeds, roll-on then back-off the throttle. If the 'knock' comes/goes/changes, then it's likely to be a conrod problem. With raising and lowering rpm, both conrod and camchain can make different sounds, so try the varying load test without changing rpms too much.
This kinda diagnostic isn't definitive, as timing knock and piston slap can do this, too. If it's well tuned with proper fuel and ignition timing, then you could rule-out timing knock.
Whether it's piston slap or rod knock, the engine needs to come apart. Then you'll find the real cause...