You must target a creature to cast Trostani’s Judgment. If that creature is an illegal target when Trostani’s Judgment tries to resolve, it will be countered and none of its effects will happen. You won’t populate.

If you choose a creature token you control as the target, it will be exiled before you populate and you won’t be able to choose that creature to copy.

You can choose any creature token you control for populate. If a spell or ability puts a token onto the battlefield under your control and then instructs you to populate (as Coursers’ Accord does), you may choose to copy the token you just created, or you may choose to copy another creature token you control.

If you choose to copy a creature token that’s a copy of another creature, the new creature token will copy the characteristics of whatever the original token is copying.

The new creature token copies the characteristics of the original token as stated by the effect that put the original token onto the battlefield.

The new token doesn’t copy whether the original token is tapped or untapped, whether it has any counters on it or Auras and Equipment attached to it, or any noncopy effects that have changed its power, toughness, color, and so on.

Any “as [this creature] enters the battlefield” or “[this creature] enters the battlefield with” abilities of the new token will work.

If you control no creature tokens when you populate, nothing will happen.