What's this on my screen, I hear one swearing (6)
I believe the answer is:
cursor
'what's this on my screen' is the definition.
(pointer on a computer screen)
'i hear one swearing' is the wordplay.
'i hear' indicates a 'sounds like' (homophone) clue.
'one swearing' becomes 'curser'.
'curser' sounds like 'CURSOR'.
(Other definitions for cursor that I've seen before include "Indicator on a visual display" , "Indicator on computer screen marking position" , "Movable screen pointer" , "Device indicating position on computer screen" , "Moving indicator on computer screen" .)