A learner painting in the open air (8)
I believe the answer is:
alfresco
'in the open air' is the definition.
(I've seen this before)
'a learner painting' is the wordplay.
'learner' becomes 'l' (as in a learner driver with L-plates on their car).
'painting' becomes 'fresco' (fresco is a kind of painting).
'a'+'l'+'fresco'='ALFRESCO'
(Other definitions for alfresco that I've seen before include "Outdoors, meal perhaps" , "where it's cool" , "Open-air" , "Meal eaten in the outdoors" , "out of the house" .)