If I had, say, a lock of someone’s hair, or a fingernail clipping, would I be able to extract enough DNA to clone them?

I don’t think from a fingernail clipping unless they really scratched themselves and got blood and tissue on it. For hair, it depends on whether or not it includes hair roots; cut lengths of hair won’t have DNA.

Note that this all presumes technology we don’t have; right now we don’t have human cloning technology - I understand they technique differs somewhat from species to species. And the cloning techniques we presently use require live cells I believe; they insert a living cell nucleus into an ovum that whose original nucleus has been removed. DNA from a dead cell wouldn’t work with present techniques.

Der Trihs has it right. Fingernails and hair are each comprised primarily of a structural protein, keratin, which is excreted from cells.

For cloning we would need nuclear DNA from cells which has not been degraded. Whether that comes from a living or dead cell isn’t so much the issue, in theory.