Thunderbolt cables generally have a lightning bolt mark, and are expensive and short and thick+inflexible. And because of that, you likely don't have any except for the one coming out of a thunderbolt dock or external GPU enclosure etc.
If there's no lightning bolt marking, it's just a charge & USB 2.0 cable, not thunderbolt. Genuine Apple Thunderbolt cables are marked, and the one you got with your MacBook for charging isn't one.
Does it have frayed rubber isolation around connectors and randomly along the cable? If yes, then it is a genuine Apple (tm) cable. If it has solid isolation ad looks good then it's probably a Chinese knockoff. :)
