Commodities are more trackable with detailed analysis then anyone might casually think. e.g. oil is a commodity but the signature of oil from certain regions is pretty visible by chemists, and one can force oil supply from trade restricted sources to at least try to mask the signature by mixing with other sources. Not perfect but you can raise the difficulty bar on commodity sourcing.
Cobalt has only one naturally occurring isotope, so I don't think you can use any tricks from chemistry or physics to track it back to the source after it has been separated from ore. Instead you need tamper-resistant supply chain documentation all the way back to the actual mine.
I'm not familiar w/ cobalt, but materials are rarely 100% pure. One might look at non-cobalt materials associated with the pure material and what ratios they're in? Again not perfect but something.
