Hi Michel,
There has been considerable debate about edged weapons from Bhutan and Tibet, as the diffusion of preferred styles has of course ignored such geographic boundaries. However, it does seem that the knoblike pommel feature is most typically associated with Bhutan. This example does seem reasonably recent, as it is embossed while earlier edged weapons from these regions are typically pierced fretwork.
The geopolitical events throughout these regions over the last half century have obviously heightened the diffusion of these weapons, and the cottage industry of 'reproduced' weapons in China has of course further clouded the issue. Nepal has become a highly travelled region for tourists in this same period and with that being the case provides a ready market for authentic weapons from these regions, as well as pervaded with Chinese made products.
As for the term for these interesting daggers, I am not a linguist of course
but I discovered the following:
"...every Bhutanese male regularly carries a knife, called a 'dossum', which he uses constantly in his daily chores".
- Bert Kerr Todd, in "Bhutan, the Land of the Thunder Dragon"
"National Geographic Magazine", December, 1952
I personally have always entertained the idea that these knob shaped swords and edged weapons, as well as the general features of the scabbards etc. of both Tibetan and Bhutanese weapons may reflect those of early Greek swords such as the phasganon and phasgana. While certainly geographically remote in relation to many regions known to have been visited or occupied by the early Greeks, it does seem that iconographically influenced weapons are prevalent over much of the Indian subcontinent and such diffusion does seem somewhat plausible. It would be interesting to hear other observations on this idea.
All the best,
Jim