Well you're certainly not being asked 'who among you knows this answer?' The writer is clearly excited about what Felix has accomplished, and the phrase invites you to ponder the different possibilities of the situation. "Who knows" phrases can often be excitatory like this, and depending on what's said before and after it, can try to lead you to agree with or think from the writer/speaker's point of view, like "you lie, you cheat, who knows what else you do when I'm not around!" Your mind could start racing with all the things you imagine the person to be doing when the speaker says this.
It's fairly common, and similar ones, clearly in a religious tone, are 'God only knows/Lord only knows....' like in 'Lord only knows how George Bush got elected to office twice!'
Other similar phrases could begin with "just think of ...", like in the above paragraph you could say, "just think of everything Felix could achieve in the coming years!" and "just think of all the children who will spread his message to others!"
(not a teacher, just a language lover)
Student or Learner