Extent of prima donna's respiration is overwhelming (7)
I believe the answer is:
breadth
'extent of prima' is the definition.
'breadth' can be an answer for 'extent' (I've seen this in another clue). I am not sure about the 'of prima' bit.
'donna's respiration is overwhelming' is the wordplay.
'donna's' becomes 'd' (this might be a standard abbreviation I've not previously seen).
'respiration' becomes 'breath' (I've seen this in another clue).
'is overwhelming' indicates putting letters inside.
'd' going into 'breath' is 'BREADTH'.
Can you help me to learn more?
(Other definitions for breadth that I've seen before include "Red bath (anag)" , "Extent from side to side" , "Liberality" , "Lateral extent" , "Width, thickness" .)