To confer knighthood for promises of cash, is questionable (7)
I believe the answer is:
dubious
'is questionable' is the definition.
(similar in meaning)
'to confer knighthood for promises' is the wordplay.
'to confer knighthood' becomes 'dub' (I've seen this before).
'for' means one lot of letters go next to another.
'promises' becomes 'ious' (IOU's, promises to pay a debt).
'dub'+'ious'='DUBIOUS'
'of cash' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for dubious that I've seen before include "Ambiguous or suspect" , "Morally suspect" , "Arousing suspicion" , "Unsure, unconvinced" , "unreliable" .)