Final answer:
The correct command to check if a turtle is visible in the turtle graphics module is turtle.isvisible(), which returns True or False.
Step-by-step explanation:
To determine whether the turtle is visible in the turtle graphics module of Python you would use turtle.isvisible() command. This function returns a boolean value True if the turtle is visible and False if it's not. It's important to ensure that you have imported the turtle module and have created a turtle instance to use this method.