A shnook is a simple or foolish person.
Calling someone a shnook is not very nice. It means they are not very smart.
Examples:
He's such a shnook, he believed everything I said.
Don't be a shnook and fall for that trick.
The shnook didn't realize he was being tricked.
The shnook thought the moon was made of cheese!
I've never met such a shnook in my life!
The shnook always gets fooled by the same trick.