A wellbore system can include a completion assembly having a completion string. The system can also include a service string that can be positioned within an inner diameter of the completion string. A location-sensing component can be positioned on the completion string or the service string. A communication link communicatively coupled with the location-sensing component can transmit signals representing a stimuli detected by the location-sensing component. A stimuli-producing device can output the stimuli that is detected by the location-sensing component. A stimuli-producing device can be positioned on the other of the completion string or the service string.