Inside the Skill Pillars? (Spoilers Farseer and Tawny Man trilogies)

['thul]

welcome to the plenty...

Well, to answer you... this may be a bit spoilerish, so its stuck inside one... read at your own peril.

may spoil many books and theories, possibly through minor details from all the 12 books released in english

There is no definite answer given. there's a high probability that it is Tintaglia. The skill pillars were built by the Elderlings, who got their magic and skills from the dragons they lived in symbiosis with. Thus one could say that the pillars are "of the dragons". It is possible, but unverified, that the black stone used to carve such is solidified memory sand/clay, which will be explained what is later, during the liveship books. Thus it would be natural for a dragon to be submerged in whatever current these pillars utilize.
There's another theory that has popped up here somewhere that it was indeed this goddess Eda, but that Eda is in fact a dragon spirit. or perhaps that the various gods are in fact all draconic in some fashion. Mind you, those are just theories.

So the answer is yes, there's theories. No, none of them have been verified 100%. It might be Tintaglia, it might be Eda, it might be something else.