Eskerrik asko azaltzearentzat.
(eta eskerrik asko zuri interesa hartzeagatik
Well, I think I will need several entries to answer... you have something like a magical gift to notice precisely the most delicate details of the language!
In principle, in norekiKO the KO particle is exactly like the KO in ahozKO. It transforms adverbs into nouns:
Mikelek jarrera zakarra dauka nirekin ari denean.
(Mikel has a rough "Einstellung" when he speaks with me)
Mikelen NirekiKO jarrera zakar samara da.
(Mikel´s "Einstellung" towards me is rather rough).
But actually that is not the way the case Norekiko is normally used. The actual use has evolved from the idea above to express itself the idea of "Einstellung jemandem gegenüber" (I`ll thank you if you have an english translation for this expression... "position towards someone", perhaps?). And in an adverbial way. The real sentence you would actually hear is:
Mikelek jarrera zakarra dauka nirekiko
It´s difficult, as I said it is a little detail (but precissely because of that I find it beautiful).
Soziatibo berdeklinatua? Well, I`m not so good with formal grammar jargon. However in this case the ber- in berdeklinatua means "again" (like in "berriz" -again-, which I guess comes from "berri" -new, anew-). It is not the ber- from "bera" meaning same/only. So: "berdeklinatua" is "twice declinsed". Upon the declension "Norekin" you add the ending "-ko". And in this particular case, the result is something more than the addition of the two cases...
norentzako and norainoko are easier. In these cases, ko is just converting an adverb into a noun
Ilea gerriraino heltzen zaio
Her hair growns down to her waist.
Hair up to the waist.
Opari hau zuretzat da
This present is for you
Zuretzako oparia auntz batek jan du. Sentitzn dut.
A goat ate the present intended for you. Sorry.
"Zerik" is never used as word in a normal conversation, I guess "zerik" is just grammar jargon used to give an interrogative adverb to the partitive case, just to paralelize the nomenclature ("Non" for the locative, "Nor" for the nominative, etc). But no one would ask
-[s]Zerik[/s] ez dago?
-Ogirik ez dago
"what is not here?"
"There is no bread"
Ogirik is a correct, normal use of the partitive, but [s]Zerik[/s] is not...
Now, for the Hurbila, Jokagabea and Jokatua, I think I know what it is, but I do not want to risk giving wrong information. Can you find me an example of those declensions?