Number of holes he has teeing off? (8)
I believe the answer is:
eighteen
'number of holes' is the definition.
'eighteen' can be an answer for 'number' (eighteen is a kind of whole number). I am not certain of the 'of holes' bit.
'he has teeing off?' is the wordplay.
'has' says to put letters next to each other.
'off?' indicates an anagram (I've seen 'off' mean this).
'he' after 'teeing' is 'teeinghe'.
'teeinghe' is an anagram of 'EIGHTEEN'.
Can you help me to learn more?
(Other definitions for eighteen that I've seen before include "majority number" , "Minus one [19A]" , "The genie (anag.)" , "Number of holes on a golf course" , "Age of eligibility to vote" .)