Look for and understand source of knowledge (4)
I believe the answer is:
seek
'look for' is the definition.
('seek' can be a synonym of 'look for')
'understand source of knowledge' is the wordplay.
'understand' becomes 'see' ('see' can be a synonym of 'understand').
'source of' suggests taking the first letters.
The first letter of 'knowledge' is 'k'.
'see'+'k'='SEEK'
'and' acts as a link.
(Other definitions for seek that I've seen before include "Ask for (permission)" , "Attempt to find; ask for" , "Try to find" , "Hunt, look for" , "Try to locate or reach" .)