Yankling Sahib is a new character who is only mentioned at the very beginning of Chapter Fifteen of this classic novel, which is of course the final chapter. This indicates that his role is incredibly minor at best and his purpose is related to bringing to a close the central narrative of the two central characters of Kim and his lama. Note the way that the chapter opens and what it tells us about the character of Yankling Sahib:
Two hundred miles north of Chini, on the blue shale of Ladakh, lies Yankling Sahib, the merry-minded man, spy-glassing wrathfully across the ridges for some sign of his pet tracker - a man from Ao-chung. But that renegade, with a new Mannlicher rifle and two hundred cartridges, is elsewhere, shooting musk-deer for the market, and Yankling Sahib will learn next season how very ill he has been.
So, as we are introduced to him, this apparently "merry-minded man" is then depicted as engaging in an action "wrathfully," which seems to undermine the cheerful impression that we are given of him. He is trying to find some sign or otherwise of his tracker, as he is expected back, but, we are told, it is only later on that he will discover why he has not heard anything.