Henry's in a painful spot on land (6)
I believe the answer is:
ashore
'on land' is the definition.
('ashore' can be a synonym of 'on land')
'henry's in a painful spot' is the wordplay.
'henry' becomes 'h' ('H' can be a synonym of 'henry').
'in' means one lot of letters goes inside another.
'painful spot' becomes 'sore' (I've seen this before).
'a'+'sore'='asore'
'h' inserted within 'asore' is 'ASHORE'.
(Other definitions for ashore that I've seen before include "on the coast" , "on terra firma" , "Home for the sailor" , "Hoarse being no longer at sea" , "Hoarse (anag)" .)