That would be "Si, lo conosco". Conoscere and sapere both mean "to know". Sapere is used for knowing facts and information, and to know how to do something. Conoscere is used to know people, places, famous people, works of art, songs, etc.
There is a good explanation and follow-up here: http://my.lifeinitaly.com/threads/5171-conoscere-vs-sapere
That's what I thought. For example http://italian.about.com/library/fare/blfare116a.htm gives 'lo' as direct object pronoun for both him and it.
No. Sapere can be replaced by "to possess an information saying" while conoscere means "to be familiar with". The sentence "I possess the information saying him" makes no sense. Compare it with "I possess the information saying it." On the other hand "lo conosco" could mean both him and it.
I checked it out, The meaning of 'Lo so' is "I know it / this".
"I know" also accepted (because there's no context)
I said: yes, I know that, and it was marked wrong. How should i say that then?
I have learned to be very careful. At first I made many mistakes because in the font used by DL l and capitol i ( I ) are too similar. Their new style for mobile devices is a bit better.