For Kaisa Evolutionary's ability, when do you choose which spell to cast from the trash - on resolution or when putting the ability on the chain?

Ruling: The spell to cast from the trash must be chosen and finalized when the "when I conquer" ability triggers, which is right after scoring the battlefield.

Sequence:

• Kaisa Evolutionary conquers and scores the battlefield
• The "when I conquer" ability triggers immediately
• The spell choice from trash is decided/finalized at this time
• The ability goes on the chain with the chosen spell