I don't know the way up the mountain (4)
I believe the answer is:
pass
This clue is a double definition.
'i don't know' is the first definition.
(I've seen this before)
'the way up the mountain' is the second definition.
(Other definitions for pass that I've seen before include "Transfer" , "Cross-mountain route; permit" , "Go by; col" , "Proceed" , "Pronounce (judgement)" .)