Is every Arduino comes with onboard compass? The doubt was came in mind after seeing Arduino documentation. I have to turn my Arduino uno robot 20 degrees without using encoders. So I surfed on Internet for how can I do that. Interestingly I found the reference available on above link. They are not saying about any specific Arduino board. So I have to know that can I do this stuff on my Arduino uno? Also I have to know is that every Arduino comes with onboard compass?
No current Arduino board comes with an on-board compass. That function description comes from the documentation for the Arduino Robot, which is a retired product.

There may be other "maker" dev boards, such as the Adafruit Circuit Playground Express which have on-board compass peripherals.