I've never seen anyone with those gems with something other than 0. Does those gems work and if yes, where do I need to put them ?
Yes, they work. I gifted a socketed hood to a friend some times ago and the current counter is 242 Sunstrike kills and 16 Tornado kills. It was 0 when I gifted him. You can socket it on any Invoker items as long as there are socket in it.
I haven't tried, but there's many many listings on the Marketplace with those gems having non-zero values, so they seem to work.