The conventional method is optical. Human vision, mental computation, muscle activation.
If this skill demands more than can be expected, then full automation.
Partial systems have been used - military FD / radar for IMC refuelling.
For a full-up system, research unmanned aircraft, but even then I am not sure that full in-flight refuelling is automatic; the manned receiver manoeuvres relatively to the auto tanker.
Whatever sensor is used it must be capable of ’triangulation’, range alone is not enough to determine spatial position.