Fern seemed off in a world of her own.
Here off means slightly abnormal or not quite sane and in a world of one's own or in one's own world could describe someone is in deep thought or concentration.
Besides, I couldn’t go from planning to sock him to asking him about being a colored Chinese boy in one good blink.
Sock is a noun which usually being used in its plural as the pair of cloth we put on out feet. Here it is, however, a verb meaning to strike or hit hard.
In one blink means changes really fast.
I should keep my curiosity to myself;
I think this is a useful expression when we want to express that we are supposed not to do something.
