Answer 1

If the opponent is of higher level than you, you'll get point even after losing. Else you know what will happen. You will lose your xp like anything. Miqayel G

Answer 2

hmmm i dont know

Answer 3

if you win you get XPs
if you loose you loose XPs
if nobody win/loose, nobody get XPs

Answer 4

either a bug, or maybe only from your first challenges (when you challenge higher level user)