Yukon is an unusual point-trick game, which appears in several English-language card game books. The earliest that I know of being Vernon Quinn's "50 Card Games for Children" (1933), which asserts that it was based on an old German game and was popular during the American Gold Rush. It is played with 5-card hands, players drawing a replacement card from the stock after each trick. The jacks, known as Yukons, are the most valuable cards and function as trumps, the spade jack being highest and the others equal. Rules of Yukon can be found on Howard Fosdick's web site.
Gold-digger is a similar game found in several Scandinavian books. It is known as Guldgrävare in Swedish, Guldgraverne in Danish and Gullgravere in Norwegian. There are several differences from Yukon:
It is rare to find card players who know these games, and it seems that most of those who do know them have learned them from books. However, David Parlett tells me that card game author Andrew Pennycook learned Yukon from his father, who spent his working life in Canada and picked it up there, possibly as early as 1910. It would be interesting to know whether it is still played in Canada, or if there are any other surviving groups of players that have a continuous tradition of play (having learned from their families or other players rather than by reading about the game somewhere).
There is one uncertainty in the rules of both the North American / English and Scandinavian versions. Are you allowed to play the Yukon of the suit that was led if you have other cards of that suit in your hand? Most of the books say something like "you must follow suit, and if unable to do so you must play a Yukon", which suggests that the answer is yes. They also explicitly say that when a Yukon is led, you must play a card of that suit, and if you don't have any you must play a Yukon. However Quinn, who gives by far the fullest description, writes as follows: "The cards rank in their usual order - A-K-Q, etc. - except the four Jacks, which are the highest of all, their suits being disregarded unless one of them is led. ... If the A is led, the J will win it - or the J or J or J; but a Yukon is played only when its owner cannot follow suit."
This seems to imply that when a heart is led, you cannot play the J if you have other hearts (the suit of the Yukon being ignored since no Yukon was led), and that if you have no other hearts you can play any Yukon, not necessarily the heart Jack. That could be important if the first player leads the A, and the second player, having no hearts, trumps with the J. AS third player you have the J and J, but no other hearts. You have to play a Yukon, but if the rules allow it you would much prefer to play the spade Jack, even though a heart was led.
There are two possible ways to resolve this: (a) to find an independent and more thorough written description of the game, ideally earlier than 1933 so that we can be confident that it does not simply represent an author's attempt to make sense of the ambiguous descriptions that we have, or (b) to find a group of good players who know the game well and ask what they do. It may be of course that there was or is more than one variation of this rule.