What voltage do people use for lining and shading when using a tattoo pen?

Hi Gary,
voltage settings are always depending on your style of tattooing, the machine you are using and your personal taste. 
You should take time with your machine to find out which voltage is the right for you and the machine. Generally most artists use voltages around 7v-9v for lining (8 should be a good start) and 8-10v for shading.