Chinpokomon Location #1: “Poodlesaurus Rex” can be found during the “Detention Sentence” Quest in the ceiling air ducts of the South Park Elementary School.
Shoot it with an arrow to make it fall to the ground, so you can pick it up.
• — [Open World] Chinpokomon Location #23: “Fatdactyl” can be found in front of the the Bijou Theatre, above the ticket booth is a collectible you can shoot down with an arrow to pick it up.
• — [Open World] Chinpokomon Location #24: “Terribovine” can be found in front of the Tweek Bros. To be able to reach/walk underneath the bench there, you’ll have to use Gnome Dust to shrink in size. Once inside it’s up high, shoot it down with an arrow to pick it up.
But it turns out Poodlesaurus Rex can still be retrieved for a little while after the story Quest is over (but seemingly no longer when you get much further into the story).
Go back through the door by the Goth kids and make your way through.