He wonders if there is, perhaps, gold inside (9)
I believe the answer is:
theoriser
'he wonders' is the definition.
The definition suggests a singular noun which matches the answer.
'there is perhaps gold inside' is the wordplay.
'perhaps' indicates anagramming the letters.
'gold' becomes 'or' ('or' is the heraldic name for gold).
'inside' means one lot of letters goes inside another.
'there'+'is'='thereis'
'thereis' anagrammed gives 'theiser'.
'theiser' placed around 'or' is 'THEORISER'.
'if' is the link.
Can you help me to learn more?
(Other definitions for theoriser that I've seen before include "speculator" , "One who has convictions" , "one who speculates" , "he thinks" , "One who reasons" .)