Look into endowing missing knight with a vacant title (11)
I believe the answer is:
investigate
'look into' is the definition.
(synonyms)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for investigate that I've seen before include "Look into" , "Enquire into" , "Search" , "check out" , "carry out a formal enquiry" .)