1.- Meera and He calls it thing
When meera try to blank a "he call it.." that its attached to a character, can blanked it and its discarded? i believe not because the text of attachment of he calls its a gained text not a printed text.
You are correct that the "Attached character gets +2 STR" text is gained text, so blanking the card has no effect. Also, once the event is attached, it turns into an attachment as its only card type. Blanking it could not discard it, even if its attachment text was not gained text.
if i win a INT challenge with reek and for an effect die after claim, can i use its response to change reek for another opponents character?
I'm not sure what you mean by "die after claim"? Do you mean the opponent uses something like "A Lannister Pays His Debts" to kill Reek before he can use his ability? In any event, yes: You can use Reek's Response while he is moribund.
If my opponent don´t have any character to "freeze" with coldhands, Can i use him in my own characters only? im not sure because the text said choose one and..
The "if able" in Coldhands' text indicates that he can be used even if some players do not have characters to choose. His effect will work on whatever characters are chosen.
4.- Abandoned Fort
Recently i saw a reprinted version in English of abandoned fort in english that said that affects "attacking and defending house bolton characters" , this it´s true? now affects both?
I haven't seen a reprinted version, but the general ruling from FFG as I understood it was always "play what your card says." It wouldn't surprise me if they updated the English language version to match what the non-English versions say.