Ask when in doubt (5)
I believe the answer is:
query
This might be a double definition.
'ask when' is the first definition.
'query' can be an answer for 'ask' (querying is a kind of asking). I'm unsure of the 'when' bit.
'doubt' is the second definition.
(a query is a doubt or question)
'in' is the link.
Can you help me to learn more?
(Other definitions for query that I've seen before include "Doubt" , "Inquiry" , "(Pose a) question" , "Question mark (printing)" .)