What trick did buck learn from Pike which would never do at the judges household in call of wild?

Buck learned a valuable, but also dangerous, trick from Pike: how to steal. Pike, being a seasoned dog of the streets, taught Buck how to snatch food and other valuables from unsuspecting people.

This trick would be completely unacceptable at the Judge's household, where Buck was expected to be a well-behaved and loyal companion. Stealing would be a blatant betrayal of trust and would likely result in punishment or even expulsion from the home.

The Judge's household represented a world of rules and civility, while Pike's world was about survival and taking what you could get. Buck's journey in "The Call of the Wild" is about navigating these two opposing worlds and ultimately embracing his primal instincts.