One needs this to see about girl (6)
I believe the answer is:
retina
'one needs this to' is the definition.
The definition suggests a singular noun which matches the answer.
'about girl' is the wordplay.
'about' becomes 're' (common abbreviation for 'with reference to').
'girl' becomes 'tina' ().
're'+'tina'='RETINA'
'see' acts as a link.
Can you help me to learn more?
(Other definitions for retina that I've seen before include "Membrane in eye, sensitive to light" , "Where you focus" , "Sensitive layer in eye" , "Light-sensitive eye lining" , "Part of the eyeball" .)