The knowledge of the most suitable gear to use (5,5)
I believe the answer is:
dress sense
'use' is the definition.
I don't know anything about this answer so I cannot judge whether this works.
'the knowledge of the most suitable gear' is the wordplay.
I cannot quite understand how this works, but
'knowledge' could be 'sense' (sense is a kind of knowledge) and 'sense' is found in the answer.
'gear' could be 'dress' (both can mean clothing) and 'dress' is present in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
'to' acts as a link.
Can you help me to learn more?
(Other definitions for dress sense that I've seen before include "style" , "Good taste in clothes" , "Good instinct for clothing" , "What fashion icons have" , "Instinct for clothes" .)