This is the Swedish version of the TV show ’Fifteen to one’. See here.
In which context can we use känner to mean know
Känner is when you know someone. Vet is when you know or have knowledge of some facts
How do we know that this is "mest" and not "flest"?
In general, mer/mest is used for amount and fler/flest for number. Knowledge is generally uncountable, thus taking mest.
A bit like less/fewer distinction in English?