And than, new problem was I couldn't write the "encoder0Pos" to LCD 16x2 if I identify like "volatile unsigned int encoder0Pos = 0;".
Why not? That is the question that you didn't answer. Fancy footwork, though.
What happens when you call lcd.print(encoder0Pos); when encoder0Pos is properly declared volatile? Does nothing print? Or, do you get some kind of compiler error?