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' is an anagram indicator.
'gold' becomes 'or' ('or' is the heraldic name for gold).
'inside' indicates putting letters inside.
'there'+'is'='thereis'
'thereis' is an anagram of 'theiser'.
'theiser' enclosing '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" .)