The Cho Oyu is the sixth highest mountain on earth. It is situated in the Khumbu section of the Mahalangur Himal about 20 km in the west of the Mt. Everest. The Cho Oyu marks the Nepal-China border. Cho Oyu means "Turquoise Goddess" in Tibetan.
First ascent: 19.10.1954 by Joseph Jöchler, Herbert Tichy (Austrian) and Pasang Dawa Lama (Nepali).
Nepal 1983, Cho Oyu.
(imperforated stamps existing)
Nepal 2004, Cho Oyu.
The picture is showing a view from Gokyo.
The stamp was issued in the series "Nepal's Eight-Thousanders".
Nepal 2014, "Mt. Cho Oyu Diamond Jubilee Celebration 2014".
(imperforated proofs existing)
Nepal 2015, Tenzing Peak & Hillary Peak.
The stamps were issued in the miniaturesheet
"Diamond Jubilee of the First successful Ascent of Mt. Kangchenjunga and Mt. Makalu".
Tenzing peak (7'916 m) and Hillary peak (7'681 m) are the names which has been proposed in September 2014 by the Government of Nepal. According official stamp issue details of Nepal Post the two peaks are located:
Hillary Peak: 28°06'24"N,86°42'58"E
Tenzing Peak: 28°06'21"N,86°41'13"E.
These two points are summits of a mountain ridge, rising above the Ngozumpa glacier and is known as Ngozumpa Kang (or Ngojumba Kang). Ngozumpa Kang has more or less three summits, all of them lacking significant prominence: Ngozumpa I (7'916 m), Ngozumpa Kang II (7'743 m) and Ngozumpa Kang III (7'681 m).
The ridge with its summits, often known as satellite peaks of Cho Oyu, is stretching from the main peak of Cho Oyu towards northeast connecting Gyachung Kang (7'952 m).
Other sources (wikipedia and google maps) are locating Hillary Peak at 27°57'31"N 86°54'34"E, which is one of the seven summits of the Nuptse ridge (Nuptse Shar III, 7'695 m).
However, the image of the postage stamp does not look like the crag of the Nuptse ridge. It looks like the view from the area of Gokyo settlement towards Ngozumpa Kang III (see also Cho Oyu stamp 2004).