Using ruler to wrap present is shrewd (7)
I believe the answer is:
knowing
'shrewd' is the definition.
(I've seen this in another clue)
'using ruler to wrap present' is the wordplay.
'using ruler' becomes 'king' (I can't explain this - if you can you should believe this answer much more).
'to wrap' indicates putting letters inside.
'present' becomes 'now' (both can mean the current period).
'king' enclosing 'now' is 'KNOWING'.
'is' acts as a link.
Can you help me to learn more?
(Other definitions for knowing that I've seen before include "Understanding" , "State of awareness" , "Cunning" , "Experienced; intelligent" , "Arch" .)