Does Rengar Pridestalker trigger on Emperor's Dais battlefield's Sand Soldier token?

Yes, Rengar, Pridestalker's legend ability triggers when a Sand Soldier token is played from Emperor's Dais.

According to RiftJudge FAQ #9982:

• Playing a token unit counts as "playing a unit."
• While tokens are not cards, they are nonetheless "played" when created by abilities, which satisfies the trigger condition for "When you play a unit" abilities.

Why this works:

1. Trigger Condition: Emperor's Dais specifies that when you pay the cost, you "play a 2 [S] Sand Soldier unit token here."
2. Playing a Token: Because the ability explicitly uses the word "play," this satisfies the condition for Rengar, Pridestalker's "When you play a unit" ability.
3. Interaction: As established in FAQ #9982, even though tokens are not Main Deck cards, they are units that are played, and thus trigger Rengar's legend ability.