Both Kai'Sa Evolutionary and LeBlanc Legend effect trigger when you conquer. If Kai'Sa conquers a battlefield, and then you use LeBlanc conquer legend effect to make a temporary clone of the Kai'Sa, do you get to use Kai'Sa twice? One for base and one from clone?

No, you do not get to use Kai'Sa's conquer ability twice in this scenario.

1. Conquering is a form of Scoring

According to Rule 447, a player may only score (via Conquer or Hold) once per battlefield per turn. Because conquering is a form of scoring, you cannot conquer the same battlefield again in the same turn, even if you move units out and back or create a clone.

2. The Sequence of Events

When you conquer a battlefield with Kai'Sa, Evolutionary:

1. Conquer occurs: You score the point for that battlefield.
2. Kai'Sa's Trigger: Kai'Sa's ability ("When I conquer...") goes on the chain.
3. LeBlanc's Trigger: LeBlanc's ability goes on the chain.
4. Resolution: You resolve these triggers. If you use LeBlanc's ability to create a copy of Kai'Sa, that copy enters the battlefield after the conquest has already occurred.

3. Why the Clone doesn't trigger

For a "When I conquer" ability to trigger, the unit must be present at the battlefield at the moment the conquest happens.

• The clone created by LeBlanc enters the battlefield after the conquest has already been completed and the point has been scored.
• Because the conquest event has already passed, the clone does not "see" the conquest happen and therefore its "When I conquer" ability does not trigger.

Summary

You only get the benefit of Kai'Sa's ability from the original unit that was present when the battlefield was conquered. The clone created by LeBlanc's effect enters too late to trigger its own "When I conquer" ability for that same conquest event.

Note: I could not fully verify this ruling against the retrieved rules, and the exact text of LeBlanc's ability was not provided.