Danny donates to the local blood drive! In his defense he was pressured into it by his peers and parents, and wasn't able to steal back his blood before it was shipped out.
True to Fenton Luck, it ended up in the batch of emergency blood supply in the Justice League, which meant that it's paper trail was erased and by the time Tucker was able to even try to find it, it was long gone.
Cut to a few months later, and Superman gets into a huge fight.
It's bad.
He actually lost a fair amount of blood.
The reserves that they thought they had specifically for him were far lower than they anticipated.
Clark can probably survive with what they have, but ideally they'd have just one single pint more.
Out of desperation, they start testing all the blood they have in stock. Maybe, just maybe, they'd stored some extra in the wrong place and mislabeled it.
They didn't, but they do find a viable donor. It issn't Clark's DNA, but the blood is unmistakably Kryptonian by nature, and it is compatible with Clark.
Anyways, that's how Danny ends up opening the door to Pulitzer Winning Lois Lane, who wants to know if he's a secret alien.
Or; The Justice League find a blood donor in their stashes that's not only compatible with Clark, but is undeniably Kryptonian in nature. They investigate and find out it's from one Daniel Fenton, and decide to be polite about asking instead of barging in. This is a Clark who had his issues with Kon, because I know y'all love to villainize that, but has grown past them, apologized, and is on good terms with Kon. His issues weren't really with Kon being a clone, they were with him seeing who he could have been if he hadn't been raised by his parents, and also his DNA was taken without his permission and used to create a person. He gave Kon his Kryptonian name and accepted him as a person, hero, and Kryptonian. Please. Please stop taking the easy way out for a villain and slapping it on Clark.