You'll find the blueprints in Nate's locker, after you know his combo, which is located on the comic strip, you found all the pieces to. I'm not sure what to do after that.
in the locker
On 24 Carrot Island, the vent diagram is in a window near the roof. On Big Nate Island, the school blueprint is in Nate's locker. The secret map to the Time Capsule is under a rock on Seal-Saw Island.
They are in Nate's overstuffed school locker, second floor of the school. The combination is 9305 (entered vertically), which you learn from assembling the comic book pieces. The blueprint shows there is a secret room behind the Detention Room.
On Big Nate island the three girls stand on the playground to the right of the school .
The school is to the right of Main Street on Big Nate Island. The four main areas are Main Street, the school, the playground, and the lighthouse (Puffin Point).
you make a stink bomb and then you'll need the blueprints so your character knows where it leads.
near the playground
Poptropica
Up of the school.
It is visible in one of the animations for the school, but not as a separate document.
out side the school
On the powerline