How many jedi did Anakin (Lord vader) kill at in operation knightfall.

I think thousands, I think knightfall was successful only because of anakin without anakin the 501st would have been wiped out.

Wrong forum again, noob.

A hundred Knights and Masters likely around a thousand+younglings.

During the Battle of Geonosis I am pretty sure Mace took the 200 Jedi who were in the temple (minus the younglings). By the end of the war thousands of Jedi were dead. So to say there were a hundred Knights and Masters were dead when the Order lost at least 1/5th of its number is being generous.

On the other hand some sources state there were 10,000+ Jedi on Coruscant alone.

He killed probably over a hundred and less then a thousand. There's no exact count.