So Ash/Spark gives the Fool dragon's blood which Chade got. Do we know which dragon in the Rain Wild Chronicles it was? I'm not sure if it was Relpda (if I remember correctly, whichever one that made the secretary an elderling), or one of the more stunted dragons that died early in the journey. Can't recall if there was a yellow dragon which I believe was the color of some of the elderling features the Fool gained.
As @yasskier mentioned in the comment, it is not obvious from any book.
In my opinion it is more likely to come from Icefyre/Tintaglia resulting from the attack on them by humans in City of Dragons, or from time Icefyre was iced in the Outislands. There is no mention of any other interactions of humans with dragons and the detailed story of the Rainwilders with the dragons the only dragon blood stolen is accounted for.
But again, this is just a guess.