Scientist initially examining old journal, in essence (9)
I believe the answer is:
geologist
'scientist' is the definition.
(I know that geologist is a type of scientist)
'initially examining old journal in essence' is the wordplay.
'initially' says to take the initial letters.
'journal' becomes 'log' (a log is a journal or diary).
'in' indicates putting letters inside.
'essence' becomes 'gist' (synonyms).
The first letters of 'examining old' is 'eo'.
'eo'+'log'='eolog'
'eolog' placed into 'gist' is 'GEOLOGIST'.
(Other definitions for geologist that I've seen before include "Specialist in the physical history of the earth" , "One studying the earth's crust" , "Specialist in the history of the earth in rocks" , "One studying rocks" , "One studying the earth's structure" .)