Viewpoint on difficult ascent (6)
I believe the answer is:
stance
'viewpoint' is the definition.
(I've seen this before)
'difficult ascent' is the wordplay.
'difficult' indicates an anagram.
'ascent' is an anagram of 'STANCE'.
'on' is the link.
(Other definitions for stance that I've seen before include "Position assumed by upright person" , "position when batting" , "Upright posture" , "a driver may take on course" , "One's physical or mental attitude" .)