Skyscraper, say, erected on what? (5)
I believe the answer is:
tower
'skyscraper' is the definition.
(I've seen this before)
'erected on what?' is the wordplay.
'erected' shows that the letters should be reversed in order (in a down clue, letters go up).
'on' becomes 're' ('on' can be mean 'with reference to').
'what?' becomes 'wot' (I am not sure about this - if you are sure you should believe this answer much more).
're'+'wot'='rewot'
'rewot' reversed gives 'TOWER'.
'say' acts as a link.
Can you help me to learn more?
(Other definitions for tower that I've seen before include "Tall feature of Blackpool" , "See 4 Down" , "Stand tall" , "Minaret, for example" , "tug attached to wreck, for example" .)