Working out problem, I had backtracked, lacking certainty (10)
I believe the answer is:
diagnostic
'working out problem i had backtracked lacking certainty' is the definition.
I can't tell whether this definition defines the answer.
'i had backtracked lacking certainty' is the wordplay.
'i had' becomes 'I'd' (common contraction).
'backtracked' says the letters should be written in reverse (I've seen 'backtracking' mean this).
'lacking certainty' becomes 'agnostic' (I can't explain this - if you can you should give a lot more credence to this answer).
'id' backwards is 'di'.
'di'+'agnostic'='DIAGNOSTIC'
Can you help me to learn more?
(Other definitions for diagnostic that I've seen before include "Computer program" , "Indicating the nature of an illness" , "Analytical" , "Distinctive symptom or characteristic (of a disease)" .)