Genius can't be defined by IQ as nobody knows what IQ is.

And I assume here the poster means IQ as a shorthand for intelligence. IQ is mental age over chronological age but mental age remains defined by intelligence tests, and nobody knows what those assess beyond the ability to take IQ tests.

That card game reminds me of two fun party games for smart groups, Great Aunt Sally and Four Is Cosmic. Don't want to spoil those by explaining how they work but inductive reasoning is fun!

Then there are the never-ending-question parlor games where an odd situation is given, and the crowd has unlimited yes-no questions to try to figure out how the situation could have arisen. Those were popular in the 90s but I can only remember 2 of them, the naked dead guy with half a toothpick and the guy who goes back to jump off the bridge. There were others, though.