On internet it helps to find reserve currency of past (8)
I believe the answer is:
bookmark
'on internet it helps to find' is the definition.
'reserve currency of past' is the wordplay.
'reserve' becomes 'book' (booking is a kind of reserving).
'currency of past' becomes 'mark' (former German currency).
'book'+'mark'='BOOKMARK'
(Other definitions for bookmark that I've seen before include "Strip inserted between pages as indicator" , "note address" , "Link" , "It helps to know one's place" , "Reader's place keeper" .)