Can I react to Zaun Warren's Conquer trigger?

Yes, you can react to the Zaun Warrens conquer trigger.

According to the Riftbound rules and related FAQs:

1. Triggered Ability: The ability "When you conquer here, discard 1, then draw 1" is a triggered ability (Rule 383).
2. Chain Interaction: When the condition is met (you conquer the battlefield), the ability is placed on the chain (Rule 383.3).
3. Reaction Timing: Because it is on the chain, players may play [Reaction] cards or activate [Reaction] abilities in response to it (Rule 813.1.c.1).

Important Nuances:

• Conquer vs. Trigger: Scoring the point for conquering happens as part of the conquer effect itself and does not use the chain. The Zaun Warrens trigger is placed on the chain after the conquer is complete (RiftJudge FAQ #7767).
• Discard/Draw: As established in RiftJudge FAQ #1316 and #696, the discard and draw are separate effects. If you have no cards in hand, you simply skip the discard and proceed to draw the card.

This is my interpretation based on the provided rules and FAQs.