As SAKWiki said:
The unique shape of this knife was apparently developed for those unable to open a standard pocket knife with their finger nails. This shape allows the tools to be pinched an pulled open.
Unfortunately, my knife is in a very poor condition, so I have to find another one. If you have such knife (or any other with Dogbone scales) please don’t hesitate to contact me. Updated 2017-07-18 — I got it!!!