Take off the valve cover and start the engine. See if oil is getting to each rocker. Take a medium sized screw driver and move to the stationary areas of the valve train and the top of the head to see if you can pin point the noise. If that doesn't work put the valve cover back on and listen to knock.
Is it there all the time? Is it just when you step on the gas? Does it get louder when the revs are on the way up or when they are coming down. A lot of listening will tell us a lot.
By the way the screw driver will isolate and project the noise to your ear.
Have fun and let us know more
Woody