What command would you use to check if Karel is facing north?

The correct command to check if Karel is facing north is represented by the option that uses "isFacingNorth()". This command accurately reflects the typical syntax used in programming environments designed for Karel, where functions often start with "is" to indicate a condition check.

This command works by returning a Boolean value: true if Karel is indeed facing north, and false otherwise. Using "isFacingNorth()" maintains clarity of code, allowing the programmer to immediately understand that this function is performing a check on Karel’s direction.

The other options would either not conform to established naming conventions or do not exist as valid functions in Karel's programming environment. Thus, "isFacingNorth()" is a precise way to determine Karel's orientation.