When you play me, [Burn 2]. (Put the top 2 cards of your Main Deck into your trash.) When I conquer, give a spell in your trash [Flow] equal to its cost this turn. (You may play it from your trash for its Flow cost. Then banish it.)
Yes. A spell that Kennen grants [Flow] keeps its existing timing permissions, whether it has [Action], [Reaction], or neither. Playing the spell for its [Flow] cost does not change the timing at which it can be played or any permission except the zone from which it can be played: your trash.829.1.b829.1.b.2
No. You must choose a spell already in your trash while Kennen's conquer ability is being finalized on the chain.403.2
Kennen's ability and Minefield's ability trigger simultaneously from the same conquer and are added to the chain as pending items.383.3.d Their order does not change the result because every pending item must be finalized before either ability can resolve.337.1337.3337.4 Minefield therefore cannot put its two cards into your trash until after you have chosen a spell for Kennen's ability, and you cannot later change that choice.355.15
From Riftbound FAQ by Christian “Near” Ivicevic, licensed CC BY-SA 4.0.
Reviewed against Core Rules 1.5. Unofficial; not from Riot Games.