I read a lot . . . mostly for pleasure. I read lots of different genres from the classics to the lastest releases. Because of my eclectic tastes in literature, I often come across words and phrases that don't mean a heck of a lot to me and I end up looking them up sometimes out of simple curiosity or other times out of necessity to grasp the meaning.
Such is with the phrase 'everything's jake'. The meaning was easy enough to comprehend in the context of the sentence I was reading but I'd never heard the expression before. So, here we are . . .
By all indication, the idiom clearly originates in the English language . . . but is most likely not British. It basically means that all is well. It was fairly popular in North America and Australia in the early 20th century but has mostly gone the way of the Dodo bird.
'Jake' seems to be nothing more than a made up word from a time when the youth of America was bucking the system . . . mainly against the older generations. New words and phrases were popping up left and right and many of them stuck . . .
such as: mind your beeswax, don't take any wooden nickles, that gives me the heebie jebbies and so on and so forth.
So, there it is. Curiosity satisfied . . . there will be no cats killed today.