If you need to run a new ground wire because you are unsure of whether the circuit (even with some existing ground wires) is grounded then you must run the new ground wire all the way to the panel ground bus. But if the new ground wire should reach the fat ground wire (grounding electrode conductor) between the panel and the ground rod or water pipe first you can clamp the new ground wire on there.
When several things (receptacles, etc.) on the same circuit need grounding and you strung a new separate ground wire, generally they can all join the same ground wire instead of each having its own ground wire home run running alongside the others back to the panel.
When several things (receptacles, etc.) on the same circuit need grounding and you strung a new separate ground wire, generally they can all join the same ground wire instead of each having its own ground wire home run running alongside the others back to the panel.